Has the tank been allowed to cycle prior to the introduction of fish? If not, that could be what is causing it to cloud. Your filter needs to grow some beneficial bacteria(looks like brown slime) to clense the water and keep ammonia down.
I'm not sure why it happens, but it did that to my goldfish's tank whenever I did big water changes. So I began using a clear water conditioner and smaller amounts of water changes and it cleared right up.
I think it should clear up in a couple of days, it may be caused by the introduction of fish and subsequent fish food in the tank. You might try very small water changes once a week, I don't know. Anyone else care to take a gander?