1st please do some research. this is something that all basic care sheet will cover. lots of info in the forums here about care.
ya at least 2 time, but id do 3, maybe do middle meal a bit smaller, also try an get them on other foods, its good for them to be on a good diet, since they are eating blackworms, try cut up earth worms as well. once they eat those u can go to bigger pices, once they master eating a whole worm i then would cut open worm and stuff small sinking pellet food in the worm let them sit in water for a few min then feed. after a while they ate it all up an then i was able to feed pellets as well, can be a challange at times. but be sure to give them a good Variety of food, will keep them healthy an growing nicely. but please since u alrdy got one do some research they are an need diffrent things than other fish, they eat more so they poop more so more water changes need to be done. good Filtration an airation. also be sure to cover ur heaters. have the right kind of substrate, make sure u ph is stable, dont add chemicals to the water. these are just a few an they can all kill ur ray. good luck an enjoy,