Carbon Dioxide and the Planted Aquarium

For plants to thrive, they must be able to undergo photosynthesis, the conversion of carbon dioxide, in the presence of light, into food they can use to grow and flourish. The light is provided by your fluorescent aquarium bulbs, roughly 1 watt per 2 L of aquarium water as a minimum. If you want to go hardcore, aim closer to 1 watt per 0.75 litres, with bulbs changed every 6 months. Also, note that incandescent bulbs (you know, the ones with the tungsten-coiley-filament-doohickey inside) require much higher wattages for the same amount of light, and deeper tanks may require more light to penetrate all the way to the bottom. I power my 54 L (60 x 30 x 30 cm) planted tank with two 15 W T8 bulbs (one Power-Glo for sweet visuals and one hardware store Plant & Aquarium bulb because I’m frugal).

You can calculate the CO2 level in your tank by measuring the degree of carbonate content and pH levels with your favourite water test kits.

CO2 (ppm) = 3 x °KH x 10^(7.0 – pH)

The ideal concentration of dissolved CO2 is in the range of 10-25 ppm. Any less than this and your plants won’t get enough. More than this can have a negative effect on your fish.

Two easy things you can do that will increase the CO2 concentration in your water are:

  • lower the pH of your water using acidifying compounds (driftwood, peat moss, alder cones, etc.). Note that “lower” doesn’t mean “low”. Plants should be kept in near-neutral water, so don’t go too crazy! “Acid rain” = bad!
  • create a CO2 injector (and possibly a reactor) setup to add dissolved CO2 to your tank. There are lots of instructions available on the Web for the do-it-yourselfer.

What I did… [ — COMING SOON! — ]


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