Your problem is definitely overfeeding. I used to feed twice a day but have cut this to just once. Dont feel guilty about the fish still wanting more food as they will always want more no matter how much you feed them (like my kids).
I have two young discus 1 bala shark 3 tetras adn 2 dwarf gouriami's. Will one frozen nutrition cube be enough daily?
How big is your tank? Bala sharks need to be kept in groups of 6 minimum, and grow up to 35cm. Minimum size tank is 6'x2'x2'.
And to answer the question, is the block bigger than their eyes put together? As that is all they need, I feed my fish a small pinch of flake, and I have far more fish than that
I would also highly suggest you rehome the bala and discus, as discus require great knowledge in fish keeping, and are one of the hardest fish to keep because of their demands. They need to have the absolute correct PH Gh and Kh not sure what they are off hand. And I really do hope you did a fishless cycle, if not these will die very very quickly
Oh also up the number of tetra to 6-10 as they are a schooling fish