ok i got a 90 gal. and a 120 gal. i do 50% water changes on each, roughly every week. my friend rob thinks that water changes are not important to do.(i'm startin to get ticked off @ him) he says doing them will not help your fish grow or improve color or health. they just make your tank look clean. he says he's gone for 2 years with out ever doing on. oh and nitrate levels don't matter. so help me make him realize he's WRONG LOL.. thanks