What are you feeding them. Too much food can cause cloudy water. Beware of this. Also, what fish etc. You may be exceding the bio load for your aquarium, probably not. But still...
Sounds like you've got yourself a good old case of bateria bloom it should subside in a about 3 days (if it is really bad 4 days at most). Do a 10% water change each day and it should quickly disappear also cut down.
How many and what type of fish are you keeping? If you've just added a tone of fish you also need to worry about an ammonia spike and work through the cycle.
Ditto the last post. REALLY sounds like a bacterial bloom. We've all had 'em and it will go away as soon as your tank begins to establish itself.
I think your concern really should lie in the cycling of your tank and keeping track of your ammonia, nitrites and nitrates...especially since you have live fish in an uncycled tank...
What are those levels now? If ammonia and nitrates are above 0, I'd do a water change but don't sipohon your gravel b/c that's where your bacteria are trying to establish themsleves...I would change the filter out yet either (because batceria establish there too)...Ammonia and Nitrites are toxic for your fish so keep an eye on that.
this happened to me to , had to empty my tank and do it all again and seems to have cleared up my cloudy water now ,but made a silly mistake and did not clean the gravel before hand