Good morning
Per our pm, I'm going to outline some considerations the pool store may not be taking under consideration in their recommended approach, hoping to benefit others as well who find iron a perplexing issue to deal with.
While I am by no means qualified scientifically on iron treatments, I have read a great deal and tried several tactics. There are usually a lot of moving parts in metal situations, so there are accordingly different approaches.
So here's some background, followed by the recc
1. Iron in pools has two primary states....Ferric (oxidized, visible like yours now) and Ferrous (in solution, invisible.)
2. There are a variety of "reducing agents" that will essentially turn ferric (visible) iron into ferrous (invisible iron). The key components that will do this to iron are: Ascorbic Acid, Citric Acid, Oxalic Acid, Salicylic Acid and Hydrogen Peroxide.
3. Each reducing agent only works well with FC lowered to virtually zero because the products will "consume/reduce" the FC and since they're expensive, its a waste because then there's less product available to treat the stain/tint. So the acid will first send itself consuming the FC, then work on the stain with what's left. It makes more sense to lower the FC.
4. Before lowering FC to add one of these products, its best to add Polyquat 60, the only algaecide we recommend, and this is about the only time you need it
5. In general, Ascorbic Acid is favored by TFP because it isn't toxic, reports on the forum suggest its more effective for iron, and it doesn't form calcium oxalate the way Oxalic acid does. But Oxalic Acid can be used for iron to get it into a ferrous state (removing stains and tint) and is believed to be more effective with copper.
6. All of the reducing agents, at the right dose, will get the iron into solution. Once the iron is in solution, eg, invisible, you then need to use a HEDP metal sequestrant to KEEP it that way. Sequestrants DO wear off over time and need to be maintained. Shocking/slamming after a sequestrant treatment is counterproductive because it then accelerates the wear-down. Normal FC will slowly wear the sequestrant down and requires only smaller maintenance doses.
7. SO, you are on well. When you're on well, there are two key strategies: a. Prevent, if possible, accumulation of iron to staining levels, which is .3 ppm and b. Preventing staining once levels are above .3 ppm as economically as possible.
How fast the iron accumulates depends on the concentration of iron in your well water.
8. Right now, if there is ANY tint to your water, it is worth it to attempt to FILTER OUT the ferric iron because it cannot be filtered out once its back in solution. This will help you accomplish B -- using less sequestrant to prevent stains in the future and slowing the rate of accumulation.
9. So in your shoes, I would set up either a Polyfill filter or create a loop with a submersible pump through any kind of house filter to get out any visible tint you can.
10. THEN, if there is staining left, you could use a reducing agent OR at that point just skip straight to Metal Magic sequestrant, which in addition to keeping the iron in solution, has proven fairly effective at higher doses in removing fresh iron stains.
The latter treatment, if it works for you, is in my experience, easier to do and cheaper in the end and fewer people have problems coming out of the treatment without an algae outbreak. Metal Magic can be ordered fairly cheaply at
http://poolgeek.com
Here's a link to their sponge test to tel how much you'd need for stains, though you might only need a start up dose after filtering.
http://www.proteampoolcare.com/images/uploads/MetalMagicSpongeTest.pdf
Hope that helps give you the bigger picture.
I should add that the liner people probably should have recommended you truck in water for the liner change. While its expensive, it would have given you quite a bit of time before you had to work on metal management
