how high can nitrate go

[philc21]

i was wondering how high can nitrate go b4 it becomes a problem so i have a number to try to keep it under

 

[fishfreek]

Are we talking about a fish only tanks or a reef tank? if its a reef tank then try to keep nitrates below 10. For a fish only tank you could probably have them creep upward of 40 or 50. The more sensitive fish will start to be effected at that level. The more robust fish could probably handle levels upward to 80-100.