just had a stray electrical current from one of my heaters going out, so i go down there to feed, fish are all acting totally fine then i put my hand in the water and ZAP, my fingers still hurt, like 20 minutes later, luckilly it was just one of the heaters, unplugged, and its gone now. ive read about that but never had it happen till now, im actually suprised the fish are fine, considering how much it hurt my fingers, but oh well, solved now, new heater in and running. so, if you ever feel a little or in my case a big sting putting your hands in the water, its probablly a heater, damn, still hurts