Feed a variety. I wouldn't ever feed just one type of food. Even if it's a 'well balenced' source of everything. The rays need the fluctuation within the diet. I vary mine by day... and keep the food types similar to what they get in the wild.
I mix my pellets in a big tub: carnivore, massive, cichlid gold, and algea wafer - all hikari. just throw a handful of the mix in each day as staple.
I also throw in frozen prawn every other day.
Yeah earthworms, mp, and nls wafers make up my staple. I give scraps of whatever fish i bought at the store for my aro. Usually lil bits of trimmed salmon or whatever the wifey is making.
KK here is my feeding. I use most bass of a shrimp everyday but i always add something to the mixture like bloodworms, blackworms, squid, fish, nightcrawlers, and crushed pellets. Everyday i change it and often have left overs and reuse it after atleast 3 days. Is this good. He has grew about a inch or half a inch since i bought him which was like a month ago.
I feed at 3 different times of the day. Noon morning and night. I feed pretty little each time but make sure in the end most of the food is gone. The ray prefers to eat at different times of the day. I used to feed him all in one time and he just doesn't eat as much. Then 5 minutes later he is begging and begging and wen i put in food he goes crazy over it. So the little food doesn't get messy and he eats well.