I.G.
I second bacteria bloom. Funny enough it actually gets worse the more you "clean" the tank, especially rinsing the gravel is a huge no-no.
The bacteria are necessary, they break down the ammonia in the water so that the fish can live.
I would try not cleaning it at all, no changes to the water for 4 weeks. It should clear by itself in that time.
You can also try taking a sample to the pet store and have them test it for you.
Good luck!