hey gerry, use a pvc pipe when you feed the rays. in my 210, i just got a ray and tankmates are rtg, st, indo tiger, ngt and ff. all eat prawn. so i use the pvc pipe to get food down and spot feed my ray. everytime my ray sees that pipe, he comes right at it. there was no way at all that she could get any good with those monsters in my tank. try it. works for me.
also, i had a red aro with 2 marbles before. didnt do the pvc thing and my red would always eat the worms. ive had no health issues. red ate a ton of it too.