01-24-2010, 02:30 PM
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Yes it is normal, but I must just correct something. It is ammonium, not nitrates, that the plants are mainly consuming as their preferred source of nitrogen. I explain this in Part Two of the 4-part stickies at the head of this section. What little ammonia/ammonium the plants might miss, the nitrosomonas bacteria will grab, but this is very little in a well-planted tank with few fish since the plants are quick to assimilate it.
For plants to use nitrates as their nitrogen source, it costs them considerable energy to convert nitrate back into ammonium; this is why they use ammonium by preference.