Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
Where are the nitrates coming from.
No fish implies no fish food. Any livestock? Whatever you feed them probably has protein, and this gets turned into NO3.
Are you adding fertilizer? If so, quit adding nitrogen for a while (several days or a week) and see if the plants use up the nitrogen enough to bring it down to maybe 10-20 ppm.
Tap water (or whatever you use for water changes?)
A 50% water change ought to bring the NO3 down by 50%, or you could do almost 100% water change (well, say 90%), and that ought to drop the NO3 right down.
Unless you figure out where it is coming from, though, it will just come back.