A healthy female guppy (Image by: judhi)

I was in a local fish store recently, when my girlfriend pointed to fancy goldfish that was turning in somersaults as it tried to move through the water.

“That’s a funny way of swimming,” she said.

I was shocked, of course; by the state of the fish, but also because my girlfriend wasn’t actually concerned about the fish’s motion. She simply didn’t realize there was anything wrong with it.

I was inspired then to write a few quick tips for buying healthy fish, aimed particularly at newcomers to tropical freshwater fishkeeping.

Physical checks for a new fish

1. Look at the fish’s eyes

Healthy fish have bright, clear eyes and an active look about them. You may think this is a ridiculous thing to say about a fish, but with time you’ll agree. In particular, avoid fish with cloudy eyes.

2. Check its body for lumps or white spots

White spot disease is one of the easiest diseases to see on tropical freshwater fish. Look out for pin-sized white spots raised away from the body of the fish. Don’t buy any fish from that tank (or any other tanks it’s connected to – ask somebody at the store).

3. Look for complete fins and tail

Damaged fins might be a sign of disease, or they could be a symptom of in-fighting between the fish in the same tank. Fish are often packed in large numbers into shop tanks, so a bit of scrapping and minor damage is always going to occur. But as a newbie its safer to avoid any damaged fish, especially as you might be looking at fin rot and not realise it.

4. Avoid fish with missing scales

Same as torn fins, really. A few missing scales aren’t fatal, but it’s better to avoid damaged fish to be sure you’re not buying a fish with built-in problems, or worse looking at a disease. Fish with huge bite marks should be avoided completely!

Fish behaviour and tank checks

5. Active fish should be active, docile fish docile

This is hard for newcomers, who don’t know fish behaviour yet. Basically, fast-moving or active fish such as barbs, danios, and platies should be busily moving about the tank – a Zebra danio lurking around the surface of the water is almost certainly sick. On the other hand, a Corydorus catfish will often sit motionless on the substrate, while dwarf cichlids typically move with a start-stop motion. Until you get more experience, the best bet is to compare your potential purchase’s behaviour with other similar fish in nearby tanks.

6. Look out for loners

On a similar note, most freshwater community fish should be out and about, taking an interest in the tank. Any fish lurking on its own should be viewed with suspicion; even non-shoaling species should usually look like they’re aware of the tank and its inhabitants. This is only a general principle – there are many common tropical fish that will lurk under a piece of wood all day, or hide in the weeds – but when it comes to more common fish it’s a good rule-of-thumb.

7. Ask to see it feeding

Very few freshwater tropical fish that are suitable for beginner’s will respond when a few flakes or a chunk of frozen food is placed in the aquarium. Not eating is definitely a bad sign, so ask to see your fish being fed whatever it’s been eating since arriving at the store. Avoid fish that don’t eat.

Bonus tip!

Always ask to inspect your fish in the bag

A difficulty with some of these tips is that you may be choosing fish from a tank of 40 or 50 other near-identical fish, and the store assistant could catch any one of them.

It’s unrealistic to ask the assistant to capture a particular Neon tetra in a tank full of them for you, so in such instances you’ll have to accept you won’t be able to handpick each fish.

Do ask to see the selection of fish that have been caught, however, before agreeing to buy them. Look out for the physical warning signs above.

Behavioural warning signs are harder to judge, since all fish are traumatised by being caught and popped in a bag.

As I wrote a couple of times above, it’s safer to avoid tanks with any suspect inhabitants in it altogether. Plenty more fish in the sea!

Further reading:

1. How many fish can you keep in your tank?
2. Tropical Fish How To Guide
3. Choosing filters for fish tanks

Clown loach markings vary widely by fish and region(Image by Butsky)

With its attractive mottled body, amusing personality and potentially long-life, the Clown loach is a justifiably popular tropical freshwater fish.

It’s also a frequently abused one, however, with too few aquarists realizing this fish is a consummate socialiser; keeping a Clown loach alone is no better then it would be to keep a single Neon tetra.

Read on for lots more Clown loach tips.

Clown Loach Frequently Asked Questions

Where does the Clown loach come from?

The Clown loach, Chromobotia macracanthus, originally hails from Indonesia (specifically the islands of Borneo and Sumatra) although the many millions in the hobby generally originate in South East Asian fish farms.

In its natural environment, the Clown loach inhabits soft, acidic and well-oxygenated rivers. It is found in the greatest numbers in areas rich in cover and debris.

Clown loach aficionados are able to identify which region of the world their loaches originally came from by subtle variations in their markets. (See ‘further reading’ below for a link to more information).

How big do Clown loach grow?

Clown fish can grow to 25cm/10”. Aquarium specimens are usually much smaller, due to inadequate housing and diet.

Can I keep the Clown loach?

Clown loaches are a slightly more difficult species to keep successfully than their popularity implies, but they’re by no means a fish for experts. Just makes sure you meet their basic needs, and take note of their potential to grow to nearly a foot in length in a well-sized aquarium.

Clown loaches are more sensitive to poor water conditions than most popular freshwater fish. Wait until the tank is three months old before adding your shoal of Clown loaches, and keep up a regime of regular water changes to reduce nitrates, especially in the absence of plants. Don’t overstock.

• Keep at least six clown loaches together. They’ll be far happier, and you can watch their interesting social behaviour, rather than fretting over moping, sullen fish.

• The minimum tank size is 48” long for juveniles. A six-foot tank would be appropriate for adult Clown loaches.

• Water should ideally be soft, slightly acidic (say pH 6.0) and at a temperature of around 28°C/82°F, although farm-raised fish will tolerate a wide range of parameters, provided they’re in the normal range for a tropical fish tank.

• A dimly lit tank, perhaps tinted with blackwater extract, will ironically mean you’ll see more of your confident loaches. Not ideal for aquascaping, but plants will be eaten or generally beaten up as the Clown loaches mature, anyway. Focus on hard furnishings as below.

• Powerful external power filters will break down the results of the Clown loach’s prodigious appetite, as well as keeping the water flowing. Undergravel filters are not appropriate, due to the Clown loach’s requirement for a fine substrate.

Note that the Clown loach reacts badly to many fish medicines due to their tiny scales. Check the instructions; you’ll typically need to underdose your tank by 50% or more if it contains these fish.

Furnishing the Clown loach aquarium

The ideal Clown loach tank reflects their muddy riverbed home, while enabling you to see more of these sometimes secretive fish due to their feeling more at home.

• Use sand or very fine, smooth gravel as a substrate.
• Furnish the tank with bogwood, smooth rocks, coconut shells and the like. The more hiding places, the less squabbling!
• Water movement in the tank should be brisk and the water highly-oxygenated, to reflect their river habitat.

What do Clown loach eat?

Clown loaches love to rummage in the substrate for food, and an ideal diet would consist of plenty of worms and other substrate-dwelling invertebrates.

In captivity we can approximate this diet by offering a wide variety of meaty foods such as frozen bloodworm, mosquito larvae and Mysis, with the occasional treat of chopped marine animals like mussels and shrimp.

Pellet food made for catfish and loaches is fine as part of a staple diet, but don’t rely upon it entirely, or your Clown loaches will get bored and their colours may fade.

Has the Clown loach been bred in captivity?

Breeding Clown loaches is a controversial subject. Many fishkeepers with mature, fat specimens in shoals have witnessed breeding behaviour and even see eggs released, but as far as I’m aware there’s no record of the offspring from such spawnings being raised in aquaria.

The fish bred in Asia are stimulated with hormones, and spawned in large outdoor pools.

Last year Practical Fishkeeping reported that a Russian fishkeeper had bred the Clown loach in captivity, again with the aid of hormones.

Video of an ideal Clown loach shoal

(Warning: Bad music in background!)

Where can I learn more?

• Loaches.com has an article on variations in Clown loach markings
• Learn more about the Clown loach on Fishbase

Have you kept them? Add to our knowledge in the comments below (keep to information about this fish species only, please).

Further reading:

1. Clown Goby FAQ
2. Serpae Tetra FAQ
3. Purple firefish FAQ

Daphnia are fascinating - not that your fish will look twice before swallowing them!

Today’s tropical fish foods are a world away from those of even my youth. And my father’s generation had to make do with biscuit-based dried foods as the staple of choice for their fish.

The huge variety of flake, pelleted and freeze-dried food we enjoy today is a real treat for modern fishkeepers (or rather, our fish!). Add in a smorgasbord of frozen foods and it’s pretty easy to keep tropical fish in top condition.

Old-time aquarists were much more familiar with feeding and breeding live foods such as Daphnia water fleas, however, and I believe this was to the benefit of their fishes.

Wives (or husbands!) might not have appreciated shoe boxes of nasty-sounding grindalworms or vinegar eels tucked into the linen closet, but their fish often did.

Early tropical fishkeepers put much of their breeding success down to feeding a wide range of live foods. Dried foods of the day just didn’t cut it.

Even today, fish breeders swear by live foods as a method of getting their fishes in the mood.

Introducing Daphnia: The water flea that isn’t

Feed your tropical fish Daphnia just once, and you’ll never again say live foods aren’t worth the effort.

It’s true tropical fish can grow, live and die on flake food, but variety is the spice of life and their lives are undoubtedly spicier for the occasional treat of Daphnia.

Daphnia are small water-born crustaceans, between 0.2mm and 0.5mm in length. They’re not fleas; the name comes from the way they seem to ‘hop’ through the water as they swim.

Daphnia aren’t particularly pretty to look at, but if you do put them under a magnifying glass you’ll find their rounded, fused bodies are usually completely translucent, so you can see everything from eggs to their beating heart. (They are used in the study of alcohol poisoning on the body for this reason). You’ll also see the legs that most Daphnia use to filter algae from the water for food.

Almost any body of freshwater in temperate regions is liable to contain Daphnia, particularly water rich in organic matter and yet low in predators, such as a muddy wallow in a farm.

If you’ve got a wildlife pond in your garden, you’ll almost certainly see Daphnia in summer – assuming your sticklebacks and minnows don’t snap them up first.

Although as aquarists we lump all Daphnia under that single name, there are actually a great many species. Some are carnivorous, preying on other water fleas. A few species with very restricted local distributions are threatened in the wild.

Feeding Daphnia to your fish

Common Daphnia is abundant in nature and in the fish trade. You can catch your own from a local pond in spring or summer, but the easiest way to start feeding Daphnia is to buy some at your local aquarium shop, where they are sold in small bags.

Unpack a bag of Daphnia as soon as you get home, since the tiny creatures can easily die from lack of oxygen or over-heating.

Either feed them to your fish immediately, or else pour the bag and water into a shallow vessel, such as an old ice-cream tub. Put the Daphnia in a cool part of the house until you’re ready to feed your fish, which you should do within 24 hours.

Before feeding Daphnia to your fish, do a quick check to ensure there are no obvious predators in the water.

Here in Europe you sometimes find water boatmen mixed in with Daphnia. These hard-shelled crustaceans are predators, and should be removed before feeding, especially if you’re feeding Daphnia to small fry. Look out for leeches, too. The odd stray tubifex worm or similar will be eagerly eaten, but remove anything you can’t identify.

If you’ve transferred your Daphnia to a tub, then a fine-meshed fish net will enable you to capture a fraction at a time for feeding. You can even use meshes of different sizes to grade your Daphnia if you’re feeding fy.

Grow your own Daphnia

Daphnia is very easy to farm in your own garden.

Get a big wide tub, or construct a small nature pond, and strew some old vegetable peelings across the base. Wait a week or two for the water to turn green. Add shop-bought Daphnia or some you’ve captured from a local pond and watch the population explode.

One problem with backyard culturing is it can encourage mosquito and gnats, which will lay their eggs on the surface. The simplest solution is to run your net over the surface of the water every few days to capture the mosquito larvae before they wriggle to the bottom or hatch.

Feed the larvae to your fish, too. They’ll devour them eagerly.

Is Daphnia safe to feed fishes?

Daphnia is about as natural as live food for tropical fish comes, unlike say worm cultures, which can be very fatty and present dietary problems in excess. You can feed your fish all the Daphnia you can find.

People are often worried about introducing fish diseases, which in folklore can be introduced to aquariums with live food.

I’ve never had problems feeding Daphnia, and I suspect that most incidents of diseases arising in aquariums that do have issues after feeding live foods come from pollution.

That said, fish diseases are strange things, with the larval stages of some parasites using other creatures in the ecosystem as hosts.

Personally I wouldn’t worry too much – professional fish farmers feed Daphnia to their fish by the bucket load. If you culture your own Daphnia on your doorstep in a fishless pond or tub, you won’t have any problems.

Incidentally, marine fishkeepers can feed Daphnia, too. It won’t last long in saltwater, so only feed small quantities that are snapped up as soon as they hit the water.

Further reading on Daphnia

• Some tips on capturing Daphnia and culturing them indoors
• An in-depth aquarist’s guide to Daphnia

Give Daphnia a try. You might just find your fish reward you with renewed vigour and maybe even breeding.

Further reading:

1. Saving a starving sun coral
2. 10 tips on creating a nature pond
3. Serpae Tetra FAQ

Heavy feeders like these Nymphea will enjoy a rich substrate (Photo: Clay Mask)

Want a beautiful planted aquarium but don’t know where to start? You could do a lot worse than follow the excellent guide to planted aquariums that Guitarfish, one of my favourite fishkeeping blogs, is running over on his site.

The latest entry concerns aquarium substrates, which is pretty annoying for me as I was preparing a post on that subject that will now have to go back to the drawing board!

I was particularly interested in his comments about natural soil substrates, as this is something I’d love to explore in a new aquarium.

Guitarfish writes:

While traditionally, many people have recommended against using soil in the aquarium due to huge algae outbreaks, recent formulas for success have been developed to make this a viable option. [...]

The key benefit to setting up one of these tanks is that very little dosing is required on a day-to-day basis, as all of the nutrients should be present within the soil itself.

Soil substrates are not for everyone. They cannot grow plants that draw nutrients from the water column, instead of via their root systems. In addition, there is a 4-8 week preparation process of breaking down the organic material in your soil, prior to setting up your tank. Finally, even after running this process, you may or may not experience a period of severe algae while the ecosystem of the tank is established.

That said, once established, the substrate has been proven to last at least a decade.

I’ve tried a few natural solutions over the years, including using rabbit droppings as a fertiliser! But I’ve never been brave enough to go all soil. Perhaps I’ll give it a go in 2009.

It’s easy to have a lot of faith in Guitarfish’s guide, as he illustrates all his articles with photos of his own beautiful aquaria. I suggest you check out his complete guide as it unfolds.

Further reading:

1. CO2 in planted aquariums
2. How to set up a nature aquarium in a day
3. Algae control in a freshwater aquarium

CO2 is the most vital nutrient in planted aquariums

The single most important nutrient for plants is carbon dioxide (CO2). Half of a plant’s mass is carbon, and so without sufficient CO2 in your aquarium water, plant growth will inevitably be stunted.

CO2 in planted aquariums comes from three sources:

• The air, via gas exchange at the water surface, just as with oxygen
• Respiration by fish and other life, including plants when not lit
• Deliberate CO2 fertilization to encourage plant growth

What is the optimal level of CO2 in planted aquariums?

Fish don’t require high levels of CO2, and in fact carbon dioxide is toxic to fish above levels of 30-35mg/l.

In well set-up aquariums, excessive CO2 is only usually a problem if there is an overdose from CO2 fertilization. An over-stocked aquarium with poor water circulation can also suffer from CO2 build up to dangerous levels, however, especially at night. Oxygen can also become depleted; watch out for fish gasping at the surface.

High levels of CO2 are no problem for the vast majority of plants. Rather, the problem aquarium plants typically face is a lack of carbon dioxide. Too little CO2 is usually a recipe for poor plant growth, however great the tank’s substrate or lighting. In such circumstances algae will often proliferate, as it grabs the nutrients and exploits the lighting ahead of the stunted plants.

Keeping both plants and fish happy in the same aquarium means balancing the CO2 requirements of the plants with the limits of the fish to create a healthy ecosystem.

Testing the CO2 level

Aquarists don’t usually measure the CO2 level directly. Instead, we work out the pH and KH levels of the aquarium water, and cross reference with a chart to determine the CO2 concentration. (See AquaDaily’s ph/KH/CO2 chart to determine the CO2 content of your aquarium water).

Another popular method of monitoring CO2 levels is to use a CO2 constancy device or drop checker. These employ a calibrated tracing fluid that changes color as the pH fluctuates with changing CO2 levels. They sit permanently inside the aquarium, and so give an at-a-glance CO2 reading:

• blue = too little CO2
• green = optimal CO2
• yellow = excess CO2

Insufficient CO2

As a rule of thumb, a typical planted aquarium requires about 1 gram of CO2 per 25 gallons (100 liters) per day. Without sufficient CO2, plants will grow slowly, even with good lighting, a rich substrate, and the addition of other nutrients. Algae will often become a problem.

To remedy this problem, plant enthusiasts usually fertilize their aquarium with extra CO2. The aim is to ensure a CO2 level of between 15-35mg/l.

Methods of increasing the CO2 level, in order of preference:

• Aerosols, liquids or tablets that release CO2 into the water
• A DIY or shop bought yeast-based CO2 reactor and diffuser
• A pressurized CO2 system, with solenoid, bubble counter and tubes

I don’t recommend the first option for anything but a short-term solution.

Yeast-based CO2 systems work well in smaller tanks, though they do require some maintenance. You can buy them for £20 ($30), but they’re easy to make, especially if you don’t care too much what they look like.

Pressurized CO2 systems are the best choice for larger planted aquariums. They enable you to control very precisely how much CO2 enters the tank, and unlike with a yeast-based system the supply is completely consistent. The downside is mainly cost, with prices starting at around £100 ($150). The other problem is general hassle – more technology always means more things going wrong.

Yeast-based CO2 systems are very unlikely to overdose the tank, but you should test the CO2 level regularly if you want to understand the tank conditions as much as possible. Pressurized systems can easily overdose a tank and kill fish, so install a drop checker and keep an eye on it.

Note you only need to supply CO2 at night. Pressurized systems usually include a solenoid, so the supply is automatically cut off when the lights go out. There’s no easy way to stop yeast-based systems producing CO2, but they are much less potent anyway.

Excessively vigorous tank filtration will drive the CO2 you’re going to so much effort to inject straight out of the water. Air stones in particular have no place in planted aquaria.

Don’t add extra fish to try to increase CO2 levels! In the night when the plants are also respiring, the CO2 can build up to high levels, not to mention the risk of oxygen depletion and general pollution problems.

If there’s too much CO2 in the water, reduce the fertilization rate according to the manufacturer’s instructions.

Is adding CO2 essential for planted aquariums?

In a word, no. If you have have softish water and green fingers, you can grow plants in pretty much any aquarium provided there’s sufficient light and other nutrients, and you pick the correct species.

Some aquarists even make a virtue out of so-called Natural tanks, where they concentrate on trying to create balanced ecosystems with the minimum of technology and interference. One system, sometimes called ‘El Natural’, even discourages water changes in an effort to try to establish a self-regulating organic system.

But for the typical freshwater aquarist who wants a pretty tank with growing plants, fish and no plague algae, adding CO2 via a yeast-based system offers a good balance of effort to reward.

(Photo by: Wandering Angel)

Further reading:

1. Determining CO2 levels by testing the pH and KH of your aquarium
2. Soil as a substrate in the planted aquarium
3. Oxygen levels for fish and plants in a tropical aquarium

CO2 is vital for plant growth, but too much in the water will kill your fish

(Photo by: nttrbx)

Carbon dioxide (CO2) is a vital nutrient for plants, but too much is deadly to fish. You should therefore monitor your tank’s CO2 levels if you’re dosing with supplementary carbon dioxide, to ensure you are effectively fertilizing your plants without endangering your fish.

One way to work out the level of CO2 in your aquarium water is to test the pH and the carbonate hardness (KH) levels. These readings can then be used with the table below to determine the CO2 concentration of your water.

How to determine the CO2 level using pH and KH

• Test for both pH and KH using your aquarium test kits
• Cross-reference both values in the table below
• The intersection gives you the CO2 level in mg/liter

-----------------------------------------------------------
 \ pH | 6.0   6.2   6.4   6.6   6.8   7.0   7.2   7.4   8.0
KH\   |
-----------------------------------------------------------
0.5   | 15    9.3   5.9   3.7   2.4   1.5   0.9   0.6   0.2
1.0   | 30    19    12    7     5     3     1.9   1.2   0.3
1.5   | 44    28    18    11    7     4     2.8   1.8   0.4
2.0   | 59    37    24    15    9     6     4     2.4   0.6
2.5   | 73    46    30    19    12    7     5     3     0.7
3.0   | 87    56    35    22    14    9     6     4     0.9
3.5   | 103   65    41    26    16    10    7     4     1.0
4.0   | 118   75    47    30    19    12    6     5     1.2
5.0   | 147   93    59    37    23    15    9     6     1.5
6.0   | 177   112   71    45    28    18    11    7     1.8
8.0   | 240   149   94    59    37    24    15    9     2.4
10    | 300   186   118   74    47    30    19    12    3
15    | 440   280   176   111   70    44    28    18    4
------------------------------------------------------------

Important notes on CO2 levels
The optimal safe C02 level for plant growth is 15-35 mg/l.
CO2 levels above 35 mg/liter are dangerous to fish.
This method is not accurate in tanks using peat or mature aquariums with a lot of organic matter and debris.

The accuracy of this testing method depends especially on an accurate KH reading, so double check your results!

Further reading:

1. Oxygen levels for fish and plants in a tropical aquarium
2. CO2 in planted aquariums
3. How to set up a nature aquarium in a day

Fin rot is treatable without a stake through the heart, however, by improving tank conditions and using one of several different treatments as discussed below.

Symptoms of fin rot

Fin rot is fairly easy to diagnose, though ideally you want to catch it when the disease has barely progressed as it will be much easier to treat.

• The first signs of the disease are milky white areas appearing in the fish’s fins or tail, particularly around the edges.
• The fins develop a rather ragged appearance as the disease begins to eat the tissue.
• Eventually the disease eats all the clear fin membrane away, leaving just the fin rays.
• If the fin rot has affected the fish’s tail (also called tail rot), it may work its way through to the body of the fish.
• Secondary infections or diseases are common in advanced cases of fin rot, bringing new symptoms to the afflicted fish such as white cotton wool-like tufts or streaked patches of red.

If you catch fin rot early you can treat the root causes and let the fish take care of itself, which is always better than treating the whole aquarium.

Make sure you don’t misdiagnose a fish that just happens to have been bred to have frayed fins. Also, fin-nipping can cause a fin rot-like appearance in fish like guppies.

Causes of fin rot

Fin rot is a bacterial infection. It’s likely that several different bacteria cause similar diseases, with Flavobacterium columnare (previously known as Flexibacter) most often blamed. Aeromonas and Pseudomonas are also cited.

However it’s not really right to say the bacteria cause fin rot. Almost always fin rot only occurs in weakened fish, most often because of poor tank or pond conditions. Physical damage or an attack by parasites can also leave a fish susceptible to fin rot.

Fin rot often only manifests itself in one or two fish at once and it is not particularly contagious, adding more weight to the theory that a weakened immune system is required for the disease to take hold.

Treating fin rot

There are three ways to treat fin rot:

• Environmental
• Anti-bacterial treatment
• Antibiotics

Fixing the environment

Fixing the environment is the most important element by far, since if the tank is in a bad way the fish will become reinfected with fin rot in the future, not to mention other inhabitants getting the same or other diseases. Fin rot is a wake-up call that you need to sort your tank out.

Do a couple of large 20-50% water changes with clean, aged water, and try to suck up as much debris and detritus as you can. Check and clean all your filters. Give the gravel a good clean, especially if you’re using an undergravel filter.

Look out for any tank bullies that are nipping or fighting with the other fish, and either remove them or the other fish. Similarly, if your tank is over-crowded you’ll need to remove some of its inhabitants to a new home.

Using an anti-bacterial treatment

Various anti-bacterial treatments and fin rot cures are effective against fin rot if caught early enough, such as Melafix (US link).

Treatments designed for aquariums or ponds should be safe if used according the instructions. If you can though, move the afflicted fish to a clean aquarium with a simple filter for treatment, rather than treating the whole tank. (Proper anti-bacterial fish medicines should not affect ‘good’ filter bacteria if applied in a proper dosage).

Treating with antibiotics

In the US it’s common to treat fish diseases with off-the-shelf antibiotics. Ask for a treatment that’s effective against gram negative organisms – there are several, which are sold under different names.

In the UK and other countries which have a more sensible attitude towards mankind’s best defense against diseases, antibiotics are typically only obtainable under guidance from a vet. As such, they’ll only be cost-effective with expensive fish, such as large koi or marine fish. Ask your vet.

Catch fin rot early enough and you shouldn’t need antibiotics anyway; better for you, the fish, and the world.

Preventing fin rot

Fin rot can usually be prevented by keeping your aquarium or pond in good condition, as discussed.

Set your tank up properly. Once running, check your tank or pond is sensibly stocked, and make sure you’re doing regular water changes (at least 25% a month, and ideally 10-20% a week). Consider whether you need to choose a new filter if your fish a messy eaters or you’re struggling to keep the tank clean.

Finally, diet has a crucial role to play in keeping fish fit and healthy. Make sure you’re feeding a wide variety of fresh foods, and that all the fish are getting enough to eat.

Further reading:

1. Floating goldfish: Causes and cures
2. 7 beginner’s tips for buying healthy fish
3. Curing seahorses of gas problems

Don't crowd your aquarium, it can only hold so many fish

There are guidelines about how many fish you can keep in an aquarium, but few experts would claim they are scientifically exact. The two main rules of thumb on stocking an aquarium are based respectively on the surface area of the tank (which influences oxygen levels) and the tank volume (this takes pollution as well as oxygen into account).

Many other things can alter how many fish an aquarium can healthily support, including:

• The shape of the aquarium
• The filtration system employed
• Surface agitation
• Water temperature
• Tank maintenance regime
• The kinds of fish being kept

Note: You can’t stock to the maximum capacity on first setting up! If your tank can hold, say, 20 small tropical fish, you should build up to that over a period of 3-6 months, to give the tank a chance to mature without a dangerous spike in pollutants.

With those caveats in place, let’s consider the common guidelines.

Fish cm per liter / fish inches per gallon

This was the rule I was taught when I first started keeping fish, and it’s still the most common stocking guide today.

1. Calculate the volume of your aquarium in liters or gallons
2. Work out the length of your chosen fish from nose to base of the tail
3. Consult the table below

Kind of fish       Inches / gallon     cm / liter
Coldwater            1" / gallon          2.5cm / 4.55 liters
Tropical             1" / 0.5 gallon      2.5cm / 2.25 liters
Marine (reef)        1" / 4 gallon        2.5cm / 18 liters
Marine (Fish-only)   1" / 2 gallons       5cm / 9 liters

For example, a 30-gallon aquarium could hold 30″ of coldwater fish, 60″ of tropical fish, or 15″ of marine fish.

Important: I am using Imperial (UK) gallons here. To work out US gallons, multiply UK gallons by 0.83 (or just stick to liters!)

The advantages of the fish inches per gallon rule are that it is easy to understand, since most people know their tank’s volume, and it takes into account the total volume of the tank. “The solution to pollution is dilution” is an old fishkeeping phrase. Bigger volumes of water can obviously carry more fish waste such as nitrate before there’s a problem.

The disadvantage of the rule is it does not take into account the tank shape. A tall, thin tank of 40-gallons will, according to this rule, have the same carrying capacity as a shallower, longer tank. But in reality the shallow tank will offer a much bigger surface area for gas exchange. In filter-less tanks particularly, it makes a big difference.

Fish length per unit of surface area

This rule puts aquarium surface area to the fore:

1. Calculate the surface area of the tank in square inches or centimeters
2. Work out the length of your chosen fish from nose to base of the tail
3. Consult the table below

Kind of fish    Inches / sq inches      cm / sq cm
Coldwater         1" / 30 sq inches        2.5cm / 190 sq cm
Tropical          1" / 12 sq inches        2.5cm / 75 sq cm
Marine            1" / 48 sq inches        2.5cm / 300 sq cm

A 36-inch long by 12-inch wide tank will therefore hold 14″ of coldwater fish, 36″ of tropical fish or 9″ of marine fish.

The advantage of using the surface area guideline is that it takes oxygen exchange directly into account. The ‘per gallon’ rule also does (that’s why coldwater fish need more gallons than tropicals) but not so directly.

The disadvantage of the rule is that people aren’t so aware of their tank’s surface area. It’s easy to work out: just multiply the width of the tank by the length. But it’s harder to keep in mind when you’re in the aquarium store wondering if you can add a few more fish.

Other issues with stocking levels

This article could run forever, so I’ll just add a few more caveats and pointers you should take into account.

Water displacement because of decoration means your tank won’t hold as much as its theoretical volume. Take off at least 10% to account for gravel, rocks, lots of bogwood and so on. With a very heavily furnished tank, take off 15%.

Different fish need a different amounts of space. Active fish like tangs or danios require more swimming room then relatively static fish like clownfish or neon tetras. Many fish require a certain-sized territory. For instance, I’d only keep one pair of dwarf cichlids in a two-foot freshwater aquarium. These measures have nothing to do with theoretical volume.

Big fish need more room than the equivalent number of little fish. Two six-inch long catfish will require a much bigger tank than 12 one-inch tetras. Their biological load is greater, and they’re messier eaters.

You can generally ignore shrimps, snails, plants and inverts when making your calculations, as they have a small biological load and often contribute to the tank’s carrying capacity (such as plants which oxygenate by day or critters that clean up detritus). Two caveats: In large numbers they will make a difference (such as a snail infestation in a tropical tank), and marine inverts can be more sensitive to poorer water quality (hence the lower stocking suggestion per gallon above).

Strong water circulation, big filters, airstones and so on can increase the stocking level of your aquarium, but I wouldn’t recommend it. Better to have healthy fish with enough room to roam unmolested than to cram in another fish or two and risk disease and infighting.

Remember, these are just rules of thumb. Erring on the side of caution is always the best policy with aquariums, and an under-stocked tank is far easier to keep in good condition than even a slightly over-stocked one.

Further reading:

1. Choosing filters for fish tanks
2. Video guide to setting up your first tropical fish tank
3. Coldwater marine tank in Norway

The Java moss growing on bogwood softens the decoration in this tank

(Photo by: nttrbx)

Ever since the Japanese aquarist Takashi Amano came to prominence, growing plants on bogwood has become part of getting that essential natural look in a planted tropical aquarium. Such plants soften the lines of the wood, and add a wonderful sense of layered drama to the tank.

Plants that grow on bogwood are often among the easiest plants to grow in aquariums, too, with Java fern in particular requiring less light than many other species. The hard part is getting the plants to attach to the wood, but it is not too troublesome if you’ve nimble fingers and a bit of patience.

Here’s how to grow plants on bogwood in five easy steps.

1. Select your bogwood in the aquarium store.

Buy proper aquarium bogwood, so it won’t leach impurities or rot in your tank. Look for interesting shapes, and don’t get carried away with huge pieces if your tank is a small one. That said, larger wood certainly has more presence, so don’t buy pieces that are so small they’re lost in the tank.

2. Wash the wood

Using a hose, blast away as much dust and dirt as you can. Then soak the wood for a few days to get rid of any immediate water-staining properties.

3. Buy the plants you intend to grow on bogwood

Only a few kinds of plants are suitable for growing on bogwood. To start with look for the following:

• Java fern
• Java moss
• Bolbitis (another fern like species)
• Anubias

4. Get some string and scissors ready

I find dark cotton works best. Ensure the string is wholly natural, so it rots away in time in the aquarium after your plants have attached themselves.

5. Prepare the plants

Trim away excessive root growth from the Anubias to encourage new growth, and pluck off dead or brown Java fern leaves. It’s worth giving Java moss a quick rinse in tank water as it can collect a lot of detritus. (Discard the water and top up the tank afterwards.)

6. Put the bogwood in position in the aquarium

Think natural and dramatic to create some interesting lines in your tank, and be sure to consider what plants you’ll be adding later. Some people tie the plants to their bogwood outside of the tank, but I prefer to do it in situ, with the tank substrate in place but before filling with water. If you attempt to submerge wood with plants tied on into a filled tank they will often come loose, though there’s no harm in trying if it’s only a small piece.

7. Tie plants to the wood with the cotton

Plant up the rest of your tank first, as you’ll only knock off plants you’ve tied to the wood while you aquascape. Then tie on your plants carefully yet tightly. Don’t crush the plants, but do make sure they’re secure as it’s much harder to tie them once the tank is filled. Obviously make sure the plants are facing upwards, and try and keep them out of the way of fast currents from the filters you’ll add later, as they’ll easily get blown off.

Here’s a lovely Amano-style tank that makes good use of growing plants on bogwood to inspire you:

Further reading:

1. Oxygen levels for fish and plants in a tropical aquarium
2. Algae control in a freshwater aquarium
3. CO2 in planted aquariums

If you have any more tips to add after reading, please drop us a line in the comments below!

1. Use plants instead of a filter

Setting up a new tank to grow plants? If you’re already spending money on decent lighting and a good quality substrate to help ensure your plants thrive, you may be able to save money by skipping the filter.

On her excellent natural aquariums website, Rhonda Wilson explains how she uses plants to keep her tropical tanks naturally sweet:

There are several reasons why I enjoy natural aquariums as opposed to those that are mechanically filtered. I find the equipment to often be distracting from the beauty of the tank. I’m interested in the interaction of different factors that make up a living system.

I know some people really like to play with all the aquarium equipment and that’s OK if you like to collect equipment. I prefer collecting different types of plants, fish and invertebrates to go in my tanks.

Here’s one of her articles explaining how to set-up a natural aquarium.

2. Use rabbit or guinea pig droppings as plant fertiliser

Filled your tank with plants but worried about the cost of expensive German fertilizers? Some plant enthusiasts swear by using rabbit or guinea pig droppings as targetted fertiliser tablets.

Dry them out in the sun, and then bury a couple in the substrate near big specimen plants like Amazon Swords and Cryptocyrenes. Go slow at first, and don’t overdo it.

Don’t use any other animal waste as it won’t be appropriately constituted and could pollute your tank.

3. Build your own DIY stand

Most aquarium stands are absurdly expensive for what they are – four or five pieces of machine cut, man-made wood, stuck together with screws

If you’re at all handy, there are loads of guides on the Internet on how to build your own stand. Here’s a few to get you started:

• A DIY stand plan generator to suit any tank size
• A guide to making joints to support the weight of a fishtank
• Plans for a heavy-duty stand you can scale to your needs – it looks like it could hold up a house!
• Here’s a 4-foot aquarium cabinet step-by-step guide

4. Get your fish for free

Ever moved house and had to give your fish away for free? I’ve done this more than once, and I know others have as well.

Generally you’re forced to push your homeless fish onto aquarium-owning friends, or even return them to a shop who reluctantly takes them off your hands then sells them the next day. (A man’s got to make a profit, I suppose.)

This is the age of the Internet, however, and there are countless opportunities for you to advertise your need for particular free fish in your local geographical area. Craigslist and Gumtree are two ad services, or you could simply post your requirements in an aquarium forum.

If you’re after livebearers you will be inundated with offers. I bought three supposedly female platies last summer. I now have about 20 platies in one of my tanks, and they’re still breeding. I can’t give them away fast enough!

5. Turn down the temperature

Many tropical freshwater fish are quite happy at temperatures of 21°C / 75 degrees Fahrenheit, yet are kept at 26°C or higher. A few do require higher temperatures, most notably discus and some South American tetras, so be careful.

If you check the lower safe range of the fish you keep, you may find you can bring the temperature down by a few degrees, which may stop the heater going on at all for most of the year in a centrally-heated house.

A few fish kept as tropicals, such as White Cloud Mountain Minnows, actually prefer no heater at all – an indoor unheated tank will suit them fine, which will save you buying a filter. And coldwater fish like goldfish certainly shouldn’t be kept in heated tanks (but people do).

Got a reef tank? The blog glassbox-design posted some tips on cutting costs earlier this week.

Further reading:

1. Five ways to turn your iPhone into an aquarium
2. Soil as a substrate in the planted aquarium
3. Algae control in a freshwater aquarium