Large water changes input

[waynemah]

Originally Posted by sirruckus

actually I haven't cleaned the canister filter - all sponge material etc. has been removed, only the ceramic balls are inside.

The Ceramic balls might be the cause of your nitrates... If you have room in your sump, you might want to consider sourcing a zeovit reactor, use the zeo media and go on the base system (Start, Bak, Food). It's a fairly proven system and well supported.