Rays aren't fragile.. they are usually half-dead before purchase. You're Motoro is probably the hardiest fish you have..
Do you think you could of had a pH swing? With the new addition of the ray you've been feeding alot, so your nitrates could be higher than usual over the 4 day intervals.. with nitrates and fish waste in general being acidic, it could of lowered your pH, and a large water change could of had it 'jump' on you, causing the behavior in the ATF..
Was it swimming oddly, loss of equilibrium almost?.. hovering at the surface, gasping.. occasionally darting into things? any barrel rolls?
Do you think you could of had a pH swing? With the new addition of the ray you've been feeding alot, so your nitrates could be higher than usual over the 4 day intervals.. with nitrates and fish waste in general being acidic, it could of lowered your pH, and a large water change could of had it 'jump' on you, causing the behavior in the ATF..
Was it swimming oddly, loss of equilibrium almost?.. hovering at the surface, gasping.. occasionally darting into things? any barrel rolls?