Originally posted by meemmoo
filter's produce Nitrates. Is that correct?
Incorrect. All waste in the tank (uneated food, fish waste, etc) eventually breaks down and creates nitrates. The filter media may "house them", but it does not produce them.
What your LFS was probably trying to say is that you don't necessarily have to run a filter if you have enough LR, a skimmer, and water movement (powerheads). If you have all those things, the only advantage of a filter is mechanical filtration.
As the other postings said, water changes will keep nitrates down.