ok i wouldent say im completly new to this i some things...but anyway i have a 55g tank running a fluval 404 and a duel bio weel hang on back(more than enouph filtration) i used sand for a substrate. i have a tiger oscar 6-7in , jack dempsey 4-5in and a pleco 5-6in. the tank was established and running great than all of a sudden after a water change/vacume it clouded up and have had elivated ammonium and nitrate issues right at dangerus levels...have done at leat two water changes and still not much of a change. im at a loss at what i did to cause this and short of water changes not sure what els to do. so my ?s being what did i do wrong and were to go from here