Well, it is a losing battle. Whenever it's feeding time, my Congo Tetra will normally wallop everything. They are very verocious and cleaned flake food within 10 seconds. This is between 5 Congo Tetras and 5 Denisonii. I also noticed that some Denisonii seldom go to the top to grab the flake food. Instead they stay at the bottom. They are very healthy and that made me wonder if they normally take their food the the mid and bottom of the tank?