if they are still breathing hard without them plugged in, probably not a voltage, but still wont hurt to check if you can get a voltage meter. also if you dont put your and in much maybe stress from that, or something on your hand that will hopefully go away. my chromis breath heavier than my other fish and have done so since adding 2 new fish, which don't bother them at all. maybe the powerheads just looking different and not feeling confidante in the surroundings with the new stiff in.