My pool has bad iron staining in some spots and a general dirty looking iron coating on the vertical fiberglass walls, especially the south shaded side. I just bought the house in July, and the previous owner opened this spring with straight well water at 5 PPM iron, which is where the iron comes from. Previous years he opened with soft water, but was cheap this spring, and regretted it afterwards, as he said he didn't have the staining previously. And yes, vitamin C tablets take them right off.
I need to do a major drain on the pool due to high CYA (130) next spring anyway, and given that I can get iron free and relatively low TA water pumping from the lake, I'm inclined to change all the water totally eliminate the iron and removing the need to use a sequestrant going forward. Additionally, because my well water has very high TA (450 hard, 550 softened), I have to use another water source or live with very high TA levels, as reducing it to ~100 with MA wouldn't be practical.
The question is, should I do the AA treatment this fall in preparation for a full drain next spring? My concern is that the iron might redeposit over the winter while the pool is closed due to sequestrant degradation. Also, if I do it this fall, I will need to mess around for a couple of weeks slowly raising the FC and PH levels up up again just before I close it, which seems like a lot of work for water that will be dumped next spring.
The more I think about it, the more I think it might better to wait till spring to do the AA treatment. The primary drawback will be working with colder water which means it will take longer for the AA to work. However, I'm thinking that the fact that once the stains are gone, I can just dump all the water and replace it, without worrying about sequestrants and slowly raising PH and FC will make it a lot easier and better. If I get the stains out, and then dump and replace the water, I can just immediately SLAM the new water, add CYA and essentially be done with it.
What say the experts?