Mario wrote:

My apologies -- N02 (should be NITRITES), I know that N03 are NITRATES.

and I have a background in chemical and environmental engineering . . .
Mario

I consider anything over 40ppm for nitrates too high - preferable is less than
20ppm
Ammonia & Nitrites I'd say any higher than 2ppm and you want to be doing water
changes.
Obviously you eventually want ammonia and nitrites to be 0ppm.