Looking to hear back on what stray voltage levels exist in everyones tank. If you do not know how to check, you need a volt meter, place the black probe in the ground socket of an outlet and the red probe in the water with the volt meter set to AC. You also need to unplug any grounding probe or titanium heaters as they will ground out any stray voltage. I just checked after getting the tingling sensation when I had a cut on my hand in the tank. I had 20V, found one of my K4's was causing 16 of the 20 volts, I still have 4 volts after replacing the one K4 and do not think I get it any lower as each power head, even new ones contributes .5 -1volt. By the way the tank/corals/fish showed no signs of stress before I replaced the pump.