I've got a tank with a bunch of tangs, which from what I've read, are more sensitive to voltage than most fish. If I can remember, i will check my voltage and see what I have. All my tangs are healthy and I've never had ich in the tank or on any of them... also no lateral line...whatever they call it...disease, erosion..I forget what it's called. As for heaters...I have three of the big eheim/jagers. A bit of advice...keep your receipt. The local store doesn't take them back under warranty, and eheim will NOT help you out if you don't have a reciept. I will likely be looking into another brand...one in which the manufacturer is a bit more friendly with their warranty. To me, it's a bit rediculous to make a customer keep a receipt on a $30 item for three years, then take 2 weeks+ to get a replacement. If you count on Eheim to replace your heater in the winter, you may have fish die before you get one.