Arlene- Do you really have pinfish in your tank? Just curious, 'cause of yer avatar.
As for well water, IMO, you never know for sure what's in it, as it changes over time. Groundwater flows, just like surface water. It's picking up whatever toxins , minerals, etc it comes across. There's been reports of raw gasoline and diesel coming out of people's faucets. I have a well- it's only for irrigation.I wouldn't use that nasty, sulfur and iron laden swill in my tanks.