Quote Originally Posted by river-wear View Post
My CYA is about 40 last I checked.
And you have an AutoPilot SWG. Bring it up to 80 ppm!
While you are at it please post a full set of test results. Right now I am particularly interested in your pH, TA and CH too.

The pH falls whenever I add water to the pool, so I usually have to add 1/2 gallon of muriatic acid at the same time.
Red flag here. Either you mistyped or we have a problem Houston! Exactly what is your pH AND TA right now? If the pH is reading 6.8, which is the lowest a pool test it can read and your TA is low then it is very possible that your pH is MUCH lower than 6.8 and causing damage to your pool. IF so get some borax in there FAST to bring your pH up to 7.2 for now since you just did a stain treatment and then add baking soda in very small amounts to get the TA up to 70 ppm if it is below that.


Also, if it matters I do have a pool heater but we've never used it.
If you pH is a low as I suspect it might be you could have a problem if you heater uses a copper heat exchanger. If the pH is low get your water tested for copper.

It's been four years since we had the pool refurbished (fiberglass coating over concrete) and metal stains haven't been a big problem. They started to appear as little speckles on the sides last year but I didn't do anything about it until now.
What color? Were they black? That is cobalt spotting (cobalt leaching from the gelcoat and crystallizing on the pool surface). Best preventative is to keep the CH as high as you would for a plaster pool. No guarantee that it will work however, much depends on the quality of the gelcoat they used on the pool.