But Byron brings up a good point. I had actually started a response but got sidetracked.
I was going to suggest adding some snails, nerite snails (tiger, zebra....) to compete for the food sources in the tank. If you only added food a few times I expect that these guys may have shown up anyway. These snails don't reproduce in freshwater, are fairly large and do a wonderful job of housecleaning. I have four, along with an assortment of pond and MTS, but the tigers really do wonders. I haven't cleaned the glass in months and it is clear as... well... glass. They even chowed down on a fungus I had on one of my driftwood pieces a while back.