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?

Feed those barbs the sinking algae wafers, they will eat like pigs and nibble to no end, the Congos will not even hardly bite the food.

I have huge fat rose lines being fed 1-2x a day this way with 1000 other fish in the same tank. They will eat flake, but feed then the Hikari sinking algae wafers or generic spirulina sticks, frozen worms etc.

These will grow large with room and continuous feeding.
Mine are much larger than many after 6 months. Pushing 5 inches on a couple, the others are about 3 months behind, but 4 inches and all started as small 2" fish.

So they will get full sized in about 1 year I'd say.(6-7")

Regards,
Tom Barr