I second bill's recommendation, biowheels rule! I have been using a
biowheel pro 60 (overkill in my case) on my 15 gallon tank and have
never had ammonia, nitrite, nitrate problems with it. I have had an
incredibly successful tank in my living room which uses a biowheel pro
60 on a 55 gallon tank. Man - I get tons of fancy guppies in that tank!
I even have a biowheel pro 60 lowered into a shallow tank containing
turtles and have had no water quality issues since. Go biowheel -
you'll love it! Later!