When their mouths are big enough to fit in the new food introduce it for a feeding here and there. Flakes after a couple weeks grind it up with your fingers a bit, beefheart usually about a month. If its home made I like to throw a couple of cups back through the grinder a second time at the end so make sure its extra fine for the fry. Im not sure what discus gran is but if its small enough for them to eat then introduce it to them.