100% true, a gfci/ground fault circuit interrupt and a grounding probe will be totally useless if the house is not wired for grounding properly. Take a volt meter and place it in your tank, if it shows any readings, try unplugging your electrical equiptment one by one until the reading drops to nearly zero, then you have your solution. I have found that there will be soome volyage still in the water even without any equiptment in the tank. very very low readings though. And the famous harbour freight has the volt meters for like $4.50.