what kinda filter do u have hooked up???
if u got anything other than biowheels u can always add more bb filter media like ceramic rings and stuff like that building a better bb colony will help keep ur tank healthy,
u have a pretty big stock what size tank do u have>???
u may need to invest in a new filter,
but for now to b safe,
do plenty of water changes and go grab some carbon or ammonia remover,
its cheaper then buying fish again..