09-22-2009, 04:30 PM
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Nitrate is removed through the regular (weekly) partial water change. It will not dissipate through surface agitation, as far as I know; common forms of reducing nitrate in drinking water include ion exchange, reverse osmosis and electrodialysis. In a heavily planted aquarium nitrates will remain relatively low (below 10ppm), but in tanks without plants (several) and with higher fish loads or larger fish, the nitrates will rise and can only be diluted/removed by a pwc. This is why the pwc is somewhat less critical in a heavily planted tank stocked with few fish.
The nitrate level in a heavily planted tank is low due to the plants, but the thinking that plants use the nitrates has now been shown inaccurate. The plants in fact use ammonium, which they obtain directly from the water in aquaria with an acidic pH [ammonia changes to ammonium in acidic water] or by converting it from ammonia directly in basic (alkaline) water. Some botanists also believe plants use nitrite by converting it back into ammonium. They are able to use nitrate by doing the same, converting it back to ammonium, but this is a more involved action for the plants and it is easier for them to grab the ammonia/ammonium directly, and the nitrite if needed, so they do that first.
The nitrification bacteria level in a planted aquarium is minimal compared to one wthout plants, and even moreso if the water is acidic. Plants are faster at grabbing the ammonia/ammonium that the bacteria, so the latter gets what is left over so to speak. In acidic water, nitrosomonas bacteria growth is inhibited, and below a pH of 6 it is believed to end. Adding new fish obviously increases the ammonia/ammonium, and the nitrosomonas and nitrospira/nitrobacter bacteria multiply by binary division. In optimal conditions nitrosomonas bacteria can do this every 9 hours. That means that the nitrosomonas bacteria in an aquarium can, if sufficient ammonia is introduced to warrant it, double their numbers in nine hours, and continue to do so until the ammonia is consumed--provided the pH is not acidic. But in the planted aquarium the plants are grabbing the ammonia, and while not being aware of the limit to this capability, I do know from my own experience that it is considerable. I set up my 115g aquarium (new filter and substrate) in one day with plants and some bogwood moved from the existing 90g tank; the 112 fish were all added the next day, and I had absolutely no ammonia or nitrite at all, and nitrates read 5-10ppm from the second day. What this says to me is that the plants and possibly the bacteria on their leaves together grabbed all the ammonia from the 112 fish without missing a beat.