As long as your ammonia and nitrite readings are 0, all you need to do is keep nitrates lower tan 20 or thereabout. That's assuming your tank is cycled. If you are still waiting for it to cycle, don't worry about the nitrate level too much. The important levels to watch are ammonia and nitrite. (I mean - you obviously need to keep nitrates down, but presumably you are doing frequent water changes anyway, if you are doing a fish-in cycle) You use the Tetra nitrate test kit, right? It's scale goes 0 then 12.5 then the higher levels. I suspect that even quite a low nitrate leve, e.g. 8 or whatver, shows up as 12.5 on that test. I've never had lower than 12.5 and I do large water-changes, and my fish are all perfectly fine at those levels.