Consider keeping lights off for 3 days and see if that helps. Rays tend to be skittish when something is bugging them, otherwise in my experience they have always been quite social, mine NEVER bury, can count on 1 hand the amount they have over the year and a half I've owned them. Vamptrevs questions about how they eat may in fact be another indicator of how they're feeling overall
i do notice that their bellies are still a little pink, not red. they are about 6+ inches and this is only a 125 gallon tank. maybe to much bioload for the system? i took everything out exept 9 tetras and 4 plecos. the peace river gravel is about 2.5 inches deep. this tank is very mature. I do feed up to twice a day. they only eat black worms. I cut up one leaf worm and put in 2 pellets in the black worm feeding cup to try to get them familiar with other foods but they wont touch it. Even if a pile of black worms are sitting in the gravel they would rather blow in the gravel for them then eat the exposed worms. maybe something is wrong. I do a 30% water change every 3-4 days and i try to suck out their poop (which is a ton) every day. there poop looks like a twisted streamer. (if that makes any sense) it is brown to very dark brown. their bellies are pronounced under their disks and their backs show a bump (like a full tummy) towards their tails. I have NEVER had rays hid like this. This just sucks. i have wanted black rays sinse i was a kid and now i have 3 that never swim around until the light go out! ):