Thanks for the reply! No, I have not yet tried plugging the returns and skimmer. That will be my task for tonight. Hopefully that will help me narrow down if it is in the body of the pool or the piping. I'm not sure which one I prefer it to be!

Thanks also for the idea of testing the water in the backyard. We actually have a tiny puddle that has already formed in one spot, so there should be no problem in getting a sample.

I'll post the results!