Why in the world is the tank so cloudy?

I can't figure it out. It was clear for months after the initial bacterial bloom. Now, it's been cloudy for over a month. It clears up a bit after weekly water changes, but by night fall its already getting cloudy. Any ideas are greatly appreciated. Thanks!

20 Gallon tall
Penguin Biowheel 150

Ph: 7.4
Ammonia: 0
Nitrite: 0
Nitrate: 15
GH: 6
KH: 2
Temp: 74

 

I had the same problem, the only thing that helped was an extremely fine filter floss that I changed every few days and lights off

 

Maybe run a uv sterilizer and see if it helps.

 

My 20 long ran into same issue. I added 2 small bio bags to my filter.

But it's a heavily planted tank but I think i added too much fertitlzer.

 

Are you cleaning your filter with the water change? If so, how?