Don't think moving them will in itself cause them to melt. I move mine all the time and even under different lighting from tank to tank. There must have been conditions that existed that they were not doing well under in the first place and moving them caused them to go over the edge. PH stability is a must for PEs. Even if it drops at night below recommended parameters it needs to stay constant within the low/high cycle. The PEs will get used to these changes and the additions of buffers, overfeeding (algae increase=ph drops at night), etc will cause enough of a change in ph levels to stress them.