I've had a couple corals lately doing this as well, at first I thought it was because one of my powerheads died for a few days. All chemistries are great, but did feel a mild electrical shocks when working in the tank. Glad this idea was brought up! I checked all my equipment, determined its my heater, and changed it out to a spare. Hoping to see some positive results soon!!
What's with these heaters? It was a Rena that was electrocuting my tank. The spare is an Ebo, seems to be major wonky for accuracy but hopefully it will be okay for now. I'm going to have to set temperature alarms on my thermometer. Probably good idea to set that up in any case I imagine. For the thermometer I have I can set alarms for min / max, hopefully will prevent a possible heater catastrophe.
