hi scorpion; i suggest(HIKARI) floating food sticks as a main diet as its cheaper & as a treat you can feed,crickets,meal worm chop them up if too big,
fresh or frozen krill,,frozen blood worm.

if your fish refuse food sticks or anything that is good for them,you will need to starve them until they do,eventualy they will eat most food.
every time my fish refuse food.i will not feed them & beleive me after a day or two fish will eat anything,persist & you will get your way.
you may have to do this a few times.
in the long run you will win.

cheers
chris