Ok then I stand corrected on those points. A few turnovers of the pool volume would be easily achieved during a short vacation.It wouldn't require any special charge. Plastic and fiberglass are naturally attractive to various compounds.
If you get metal stains in a pool, they will usually be most evident on the plastic steps and other plastic items.
It's a small pool with an oversized pump. The circulation is going to be pretty good.
Would you believe that many of the other chemicals we add to pool water conduct better than the salt? (Look up seawater conductivity on Wikipedia) Other minerals as well already in the water. In practice the total dissolved solids in water determine the conductivity of the water. It matters little which ion it is measuring, when ther are a bunch it averages out. Cl- ions pretty effectively also come from the various forms of pool chlorine. In the case of pool water, that pretty much fairly resistive chunk of water will actually act like a Faraday cage to stuff of lessor conductivity (like PVC) than a conductor to it. Again, I don't buy the lightning hypothesis in this case. Especially if there isn't damage to surrounding stuff....The OP says the pool has a salt system so the water should have a good bit of salt in it and salt water will conduct electricity much better than non salt water.
Any other updates on this topic? I just spent 45 minutes reading through this thread hoping to see a grand AH-HA moment at the end. Sorry for all of us getting entertainment from your bad pool situation but it is very rare to see so many TFP Experts get stumped on a topic.I have an electrician coming next week to inspect the pool. I will give an update...