Stinky water.

[sap]

I have a 55g grow out tank with 1 Magnum HOB w/ carbon, 2 Hagen 402 w/ pre max filters and 1 hydro sponge running off of 40g air pump. I am doing 50-65% water changes every 2 days and the water still stinks.... IS there a different chemical filtration I can use besides the carbon that would be more effective in removing the foul smell of the water? Possibly up the chemical filtration to something more than 250 gph?

[supersmirky]

Carbon should get the smell out. Whens the last time you changed your carbon out?

[sap]

less than a week ago... sponge prefilters are cleaned every 2-3 days. there is possibly 150 1 inch fish in there so they are producing quite a load but the 402's with the prefilters on there seems to do a good job of collecting the waste.