I have had issues with staining in the past in my plaster pool. My question is since I am on well water, every time I need to add fill water to the pool, would you also recommend at the same time I always add a metal sequestering agent?
It's a very strong possibility. It's very common for well water to have excessive amount of iron in it, so it takes extra effort to keep the iron from reacting to the chlorine in a pool. Things you can do include:
- Pre-filtering the water before it enters the pool. There are various DIY methods others have tried. You can find some at TFP by using the search feature.
- Keep the pH a bit low; perhaps 7.4 or so. Since you have a plaster pool, you have to be careful to not go too low (for too long) with pH or it can make the water too corrosive and damage your plaster. But typically iron water does better with a lower pH level.
- Try to avoid excessive (high) free chlorine (FC) levels. That means avoiding algae too, because if you get algae, you have to "SLAM" at a higher FC level.
- When those methods above don't work on their own, then a sequestrant is used and reapplied as needed to prevent the iron from precipitating-out into the water (color changes & staining).