Brian,
I used to do electrical work for a farm in my town. We would use heater tape around the water pumps in order to get water to the live stock. When I worked near a dock on the lake, we used to use bubblers in order to keep the water from freezing around the dock. I am going to assume that an airstone is like a water bubbler. Maybe they make electric blankets to wrap around the trough to prevent the frozen water.
As for stray voltage, that would be a real hot topic around here. I have seen lots of problems with stray voltage around pools. Sometimes it was caused by pin hole leaks in the Power Co. (POCO) primary underground feeders.
We would get readings between 5-30 volts around a pool. Enough voltage so that you feel a tingle when you touch metal, the pool deck and had bare feet.
