Thanks. I think the Culator is a good idea. I will first do a bucket test to see if there are metals in the water currently. I will also do some testing with ascorbic acid on the existing stains to try to verify that it will work on my stains.

I am using the Taylor 2006 test kit. I plan to take over from the pool service and test for a while to establish a good baseline before doing anything about the stains.