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!
Check out Katy's Tropical Fish Guide for more aquarium info.
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