First, that level of nitrates is not bad for a FOWLR
. 2nd, how are you maintaining the filter? Are you using it for just mechanical and chemical? You may have to cause you are a little under stocked with LR
. Just keep doing your PWC
's once a week and rinse out the sponge in old aquarium water (I think you need to keep the bacteria on the sponge going with the amount of LR
you have) if, however you could boost LR
in your tank,'then I would buy a second sponge and just replace it on a weekly basis to stop the bacteria from converting to nitrates, and just pretty much use it as a mechanical filter. Hope this helps.