Re: Ammonium or nitrate uptake

> I have measureable ammonium in my tank. Can somebody explain to me why I still
> need to add nitrates to avoid nitrate deficiency for the plants? The nitrate
> is used up by the plants but I thought that plants prefer ammonium?


You don't need to add nitrate if you have measurable ammonia/ium.
Is this an established tank? Does it have soil? If it's a new
tank, it may be that the plants are not sufficient to handle the
load of the fish. If it's a soil tank, it could be that the soil
is decaying and adding ammonia more than your plants can use.
Try to increase your plants and light. Perhaps you may need to use
a biological filter (if you have none). Removing fish and just
having the plants is also a good way to break in a rich substrate.
In that case you can let the ammonia be (no biological filter) and
the plants will grow very fast. It is a balance. I try to use as
little biological filtration as possible without getting too high
levels of ammonia. Some filtration is also important to remove
floating debris but this can be done periodically (once a month
for a day or two).

As long as there is ammonia, the plants will NOT use the nitrate
at all.