Is CA chlorine? If so your chlorine is high along with high ph which will make any metal that was in the water fall out onto the surface of the pool. United chemical is an oxalic acid. It will bring down your ph, along with your chlorine. With such a high chlorine level it may take a lot of stain treat, because the chlorine will eat up the oxalic acid. Even though your water didn't test for metals, it was in there - it can come from many things, fertilizer is one. Is your pool a plaster or vinyl or fiberglass. If it is plaster a calcium of 90 is not enough, you need 200 - 400 in a plaster pool. If it is vinyl or fiberglass 90 is fine.

I would suggest letting your chlorine fall to normal level before doing the stain treat (so that you will not need as much product) - which for a cya of 90 would be 10ppm. You can use some muriatic acid to get your ph down while waiting for the chlorine to drop - I would take it down to 7.2 - 7.4. Your alkalinity is a little high also, it should not be higer than 120. Then you can do the stain treat, which will bring down you ph and alkalinty. Post your numbers after the stain treat - let me know if all of the stains come off. Good luck.