they are in a 7x4x2 foot tank but are currantly seperated from the other fish with a divider giving them 4x2x2 foot,i use tap water as the guy i bought them off said that was what he was useing and they have been fine for the two months ive had them untill now.i dont treat the water as i fill a large containor that has two large airstones in after every change then its in there for a week before i use it,i did have them on a thin layer of sand but have now removed most of this however there is still a small amount left that appears to now be sticking to the rays,for my filtration i have two bioforce 9000l pond filters that have three sponges and biomedia [looks like lava rock]i take it in turns cleaning them as i thought this would cause less upset to the tank and they get done once every 4weeks but to be honest theres never much if no dirt in them,for airation i use an aquaone o2 plus 8000 pond pump conected up to 4 large air bombs that gives the tank loads of surface movement and im not doing anything diffrent than when i first got the rays ill try leaving the lights off as ive not done this yet and i hope this info gives you some ideas to what im doing wrong thanks again to everyone for all your advice.