I have a 25,000 gallon white fiberglass pool in service for 7 years. It has a sand filter and Hayward pool heater. I drain off 9-12” of water every fall when I winterize the pool. The first 3 years, I had the pool filled in the spring by a water truck with chlorinated city water. The past 4 years, I filled it with my own well water and added a quart of metal out after filling. I did not have major staining issues until this last summer. In prior years, I would have to use a stain remover once a year, and that would last the season.
This last summer however, I treated the pool 4 times with a powdered stain remover, and I still have a major staining problem. The brown stains are primarily out of the outlet nozzles and the walls below them, but the stains cover the entire pool. Each time, the stain remover would work great, and the stain was gone in 24 hours. The first and second times, I did not add metal out after the stain remover (a water test showed no iron or copper) and shocked it right after the stains were gone. Stains came back as bad as before. Third time, I added 1 quart of metal out and waited 2 days after stains were gone to shock. Stains came back bad as before. Fourth time I bypassed my heater, added 2 quarts of metal out and waited 5-6 days after stains were gone to shock. Stains came back as bad as before (although it took longer). Now, when I rub the stains with a vitamin C tablet, it takes the stain away, and for some reason, these small areas are not getting the stain back, even though the rest of the pool is extremely stained.
From the forum, I think I know things to try. Here is my plan and questions:
1. I will plan on draining 9-12” of water this fall as before. Do I need to treat the water this fall. Should I remove the stain this fall before draining or wait until spring? Am I adding enough metal out for a 25,000 gallon pool?
2. I will refill in the spring with chlorinated city water. How will I know if the water remaining from this year will cause a problem? Do you know how much water I can remove safely from the pool in the spring?
3. I changed the sand in the filter last year. Should I change it again? Could the staining minerals be in the sand? Am I not backwashing the minerals out enough after the stain remover?
4. Bypassing the heater did not help. Could my heater (bad heater core) still be the root cause of the problem this summer? Maybe it added a ton of copper to the water when it was hooked up, too much for the metal out to remove. I have had a chronic Ph problem in the past, the Ph staying in the 6.8-7.0 range for extended periods.
5. I realize now, the chlorine should be introduced very slowly after stain remover. I will plan on using the polyquat at the beginning of the season instead of chlorine.
Thanks for the great forum. Any suggestions would be appreciated.
