I have bad iron staining in the pool. It has been building up for the last two or three years and I could not find the source until recently. I believe it is coming from an iron ring around my underwater light. I checked the ring with a magnet and it is definitely iron. So I'll have that replaced and then acid clean the pool.
I confirmed the stains are iron by dropping three vitamin C tablets in a corner of the pool and the results were pretty dramatic. In less than an hour the area around the tablets went from a dirty yellow to a bright blue liner. It was pretty amazing. I spent a lot of time reading up on the Ascorbic Acid cleaning procedure here (thanks for posting it) and I believe I understand what needs to be done. I went to Jack's magic stuff site and read up on using the sequesterant and the part I don't like is having to test and add sequesterent on a routine basis after getting the stains off. I estimate the chemical cost (Jacks Magic Blue Stuff) to be close to $1,000 per year for my pool. That does not include the test kit ($93!) and testing supplies.
The only alternative to maintaining a sequesterent level to keep the iron in suspension, I can find, is replacing all the water in the pool. Is that right or have I overlooked something? I don't want to just pump the pool out all at once, although I've done that in the past when the liner was replaced and did not have any problem with ground water or with the sides of the pool caving in. My idea is to just put a water hose in the pool and let it overflow until the iron is below detection limits. I estimate it would take two or three weeks of running the hose 24/7.
The cost of the water will be about $300 - $600 at my rates and there will be increased costs for chlorine, CYA, and sodium bicarbonate. Those costs are worth it to me as the price of avoiding the aggravation of having to monitor another parameter for the pool. Does this sound like a reasonable thing to do and are there any alternatives?