Could coldwater aquariums be the next big thing in marine fishkeeping?

Non-photosynthetic coldwater corals are definitely not for beginners

Photo by: Steve Weast

Blame my holiday, but I’ve only just caught up with the latest issue of Advanced Aquarist, and its article on coldwater marine aquariums.

It’s a pretty good read, particularly if you want to know more about the physics of heat and light that leads to such different coastal habitats in the chilly North compared to that enjoyed near the equator:

Due to differences in seawater density (the result of different seawater temperatures), sea level is approximately 8 cm (3 in) higher at the equator than it is at the poles. The resulting slope is sufficiently steep enough to move enormous amounts of water to the poles. Cooled, denser polar waters sink and creep back to the tropics from the deep.

Another, more complex, system of currents is driven by the planetary wind system. At the equator, moist, heated air rises and drifts toward the poles. Much of the moisture is lost by rain as the air cools en rout. At about 30° north and south, this drier, cooler, denser air sinks. It is then reheated and rehydrated, it rises again and flows to about 60° north and south were it produces yet another high-precipitation area. These much cooler winds flow into the polar regions.

There’s lots more where that came from, as well as a discussion about whether coldwater marine keeping could take up some of the demand currently exerted on tropical reefing, and what the consequences might be.

Keeping coldwater marine creatures

While the article touches on one big problem – the limited supply of livestock – there’s not much else about the practicalities of coldwater marine fishkeeping.

I’ve kept coldwater marines here in the UK, and by far the biggest problem is keeping the tank cool.

It’s often not enough to simply use a chiller, as you would with a tropical reef system. With a reef tank you’re only looking to lower the temperature a few degrees to keep it around the 24°C range, whereas with a coldwater tank you want to go much cooler for long-term success.

If you can, it’s therefore best to head underground into a cellar or basement to setup your coldwater tank. Failing, that a naturally chilly North-facing room that’s cut off from the rest of your house might work.

Once you’ve got a cool tank, use low wattage pumps like streams and try to keep heat out of the aquarium. The Ecotech pumps, which mount the hot element outside of the tank, would be ideal.

Lighting isn’t a problem traditionally for coldwater tanks, but that’s because few of us have tried to keep many seaweeds. As the Advanced Aquarist author says, a proper temperate habitat would be dominated by kelp and the like. That said, you’d probably get away with T5s or better yet cool running LEDs in shallow tanks.

Use a big tank if possible, partly because coldwater animals really like to eat, and also their oxygen requirements are higher so if you want to keep multiple fish and the like, a bigger tank is the way to go.

Filtration is best achieved using the old marine system stalwarts of undergravel filters (possibly reverse flow) and/or an external wet-dry filter.

Use a big skimmer, since your tank will generate lots of waste. I’d consider exploring an algae filter for nutrient export, though I don’t know if anyone has done that yet.

Want to know more? I looked at Jon Olav Bjørndal’s Scandanavian coldwater set-up in my great aquarium blogs post. It’s well worth checking out. Steve Weast’s coldwater system, as cited in the Advanced Aquarist text, is also an inspiring read.

Responsible note regarding coldwater corals

I know I probably bore some readers banging on about conservation, but nevertheless I have to say I hope keeping coldwater corals doesn’t take off until we understand a lot more about them, particularly their care and growth rates, and ideally propagation.

Coldwater corals are generally solitary or form far smaller colonies than their tropical brethren, require feeding with planktonic organisms, and as I understand it grow very slowly. A few experienced fishkeepers like Steve Weast developing techniques is one thing, but hordes of us suddenly donning wetsuits to plunder a limited supply would be bad news.

Besides, there’s plenty of other cool coldwater creatures to keep, including various seaweeds, molluscs, crustaceans, worms and, of course, fish!

Read the Ultimate Secrets To Saltwater Fish And Invertebrates.