I recently bought this house that had an inground pool (~20,000 gallons) and hot tub (~2500 gallons). I spoke to the old pool company who serviced the pool for several years and he mentioned that he painted the spa about a year ago. The spa always had a slight yellow color to it which I attributed to the paint. The pool has always been clear/blue.
Fast forward to this past weekend... we had a party and about 10 people+ were in the tub. I noticed when I was testing the water 2 days ago that the spa was much much clearer. The closer I looked, the more I saw the yellowing was gone. There still is some remaining stains on the side, etc. It appears as though I had iron staining the whole time. Last night I poured some stain control in and isolated the spa and ran the filter over night. The stains appears to be lightened some. I think this confirms iron staining.
My question is, can one use muriatic acid vs. ascorbic acid in the spa and just circulate and brush? Wouldn't this lift the stain as opposed to ascorbic acid?