We moved just over two years ago to a house with an inground pool. I've used tablets exclusively as did the previous owner. The previous owner did not balance the water aside from keeping chlorine in it. He told me he never worried about pH, alkalinity, etc. I decided I was going to balance the water in all aspects. The first year, I started to balance the water and got a lot of iron staining on my white fiberglass pool. I learned of vitamin C to remove it and it worked like a charm. Then it came back. Talking to my pool store (locally owned company), I used Revive, to help remove the iron which it did. The settled sediment at the bottom was rust colored. Place metal out in the water and it was good the rest of the year. The pool store tested my water in the pool and the source of water (city water) and none showed any iron. Our house used to be well water so I'm assuming that's where the iron came from. Last year when I shocked the pool with chlorine to open it, the iron stains came back. Used Vitamin C, revive and metal out and stains stayed away all year. This year when I opened it, again, same thing. Used vitamin C, revive, and metal out and no more staining. I pretty sure the high level shock is what caused the iron to stain my pool. Now that I have researched and want to use the methods here, mostly due to high CYA levels which is another story all it's own, is SLAMming my pool going to cause the iron to stain again, and then if I use Vitamin C to remove the stains, it takes the chlorine out then I'll have to start all over. That's why I'm nervous about doing the SLAM process.