first of all, can you give us more information on the tank itself?
Ok... If the tank is directly opposite or near a window, and heaps of light is able to get into it; try and block the light from the window.
Or you can try keeping the tank in total darkness if you want to...
Or, a more simple method would be to buy a uv steriliser which kills off the bacteria, leaving you with clean, clear water..
Hope that helps!
how often do you clean the filters? How much do you feed? What do you feed?
wait.... do you mean you feed flakes 5 times a week or 5 times a day?
ok. This happened to me, i followed the rules and everything, when i got it i did a black out, 2 fish died in the black out, no idea why, the closest explanation is the filter strainer fell off and they got sucked in the filter. I tried no more feeding, didnt work, i tried no more fertilization, didnt work, in the end i bought the darn uvs.