Non-messy foods for my large BGK?

I am looking for foods for my 9inch Black Ghost Knife that when i put them in the water for him don't break up into a hundred pieces and dirty up the tank. I have been trying Frozen beef heart cubes, however when they thaw in the water they start breaking up all over the place and the next morning i have the small left over pieces all over the tank. The tank at this time is only for him so i don't have any scavengers in there just yet, until i upgrade. I adopted the BGK on kind of a quick notice. Any suggestions?