A friend of ours in Virginia had that happen several years after her pool had been installed. She discovered it when her dog avoided a particular area of the the pool. They called the PB who did every conceivable check of the system and couldn't find anything wrong but was able to show some electric leakage in the water. I'm not saying this right, it's been a few years. They finally called the electric company which discovered an issue with some ground wires in lines they had installed recently. You might want to contact your utility company.