It is the floor. Thanks Tim!
I've seen things you can buy that allow you to put a puck or Vit C on the floor and see what happens. Does anyone have any suggestions or recommendations of products that would be helpful here? I think I understand that organic matter would be leaves etc. What about metal, where would that be coming from, if on the bottom, since I think the bottom of a vinyl pool is not metal, so what would that be coming from? Thanks.