Semi-transparent patches floating on water

[chem geek]

I seriously doubt the chemist put anything with mercury into the pool. He probably said something like adding an algicide with metals in it, maybe even saying "heavy metals" so that probably means copper. If you can still contact him, then ask him EXACTLY what was the "extra strong shock formulation containing mercury".

[Pappy]

I don't know how accurate they are, but you can buy mercury test strips on Amazon for about $20. I think if I were in your position, I'd spend the money and be for SURE.