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Roger's Aquatics Pages |
The nitrification which occurs in your tanks will increase the amount of Nitrate in the water. This is important because both Nitrate is toxic in high concentrations and will build up with time. Concentrations can be bought down with partial water changes, it is also absorbed by plants.
Nitrate is found in tap water, sometimes at quite high concentrations. This would not normally occur naturally, as Nitrate is rapidly absorbed by the environment, but it comes from agricultural run off. With high levels of Nitrogen based fertilisers being added in modern agriculture this will remain a problem for the foreseeable future. It is so bad in my area that, in tanks where I have actively growing plants, the Nitrate concentration can be increased during a partial water change.
One solution to this problem is to use denitrification. This is a biological process where bacteria convert Nitrate to Nitrogen or Nitrogen Dioxide. The bacteria that carry out this process are Heterotrophic – that is they "eat" organic materials, much as we do, and burn hydrocarbons for energy. Bacteria are much less fussy that higher organisms about what carbon based chemicals they will use, and they carry out a number of different processes. The bacteria we are interested in are those which burn the hydrocarbons using oxygen, to give carbon dioxide and water.
Many such bacteria can live without oxygen by getting the Oxygen from elsewhere. One such source is Nitrates. They split the Oxygen off and use it to burn the Hydrocarbons, and release Nitrogen or Nitrous Oxide. This takes energy, but less than they get from burning hydrocarbons, so it is only worth doing if oxygen is in short supply – what are known as Anaerobic conditions. The trick is to arrange it so that some of these bacteria find that they are trying to live in Anaerobic conditions.
There are a number of ways to achieve anaerobic conditions in the aquarium. If your gravel is deep and you don’t use under gravel filters then areas may become anaerobic and remove Nitrate from the water. Many filter mediums, such as some ceramic media and sintered glass allow bacteria to grow inside them, The insides then become anaerobic and help to denitrify the water.
The final option is to buy or build a denitrifying filter. Building a denitrifying filter at home is surprisingly easy.