The nitrate problem is researched extensively by diana walstrad. You can find information on the very good book. (she only wrote one good book, made a lot of money i think)
The summary is this, plants do consume nitrate but they will need to convert nitrate to ammonium first. hence if you have ammonia in the water, they will consume ammonia first then do the conversion once ammonia is depleted.
A very neat device is discussed advently here in the forum.
It is called the denitrator. Nitrate levels as high as 100pm can be reduced or eliminated altogether. The advantages are many with good control. My experience to share here is, probably more relevant to the brothers who have tried it than starters, use a moderately high flow rate first. not the other way around. Then slowly reduce it overtime.
