I hope you have a good working filter in the aquarium. Also this clouding can occur if there are too many fishes for the size of your tank. There a solution called AQuaclear available at the fish shops , a few drops can coagulate the dirt and the filter will remove it.

Also you can change the water partially..like half the tank.

I hope that helps. 

We are only children once...but we can keep the child in us forever.