Hello all. I'm new to fish keeping. I have had a 96 gallon freshwater tank with 12 africans and two catfish established for about one month. I have done one 20% water change. In the last few days the sump has developed a thick white/tan foam. I have searched the forums, and have gotten some indication that this could be caused by overfeeding (decaying organics in the water), but I have not found a definite answer. I have been feeding flakes twice a day, enough to be eaten in a few minutes and also dropping 2-4 algae thins to the bottom of the tank. Too much? Other possible causes? Should I be worried?