nitrate levels for plants and fish...

Hi folks,
my nitrate levels in a 120 are pretty high (for fish anyway - around 40-50),
but the plants seemt o be pretty happy - they've really taken off with the
higher levels.... anyone else having this problem? if so, what taret levels
do you shoot for?

the fish seem more or less OK - no deaths, and no real indications of
problems, but before I find some sort of nitrate scrubber, I figured I'd ask
and see what the impact on the plants would be if I lowered the levels..
thanks
-_JD