I have posted in the past about phosphates being introduced into a pool by adding sequestrants with phosphonates in them. So recently I've been noticing that some pools after being treated for phosphates, will leave iron stains behind. Usually they are very faint rusty colored areas left behind where the precipitate settled into piles. So I'm wondering if by treating phosphates, I'm getting rid of the sequestrant, and allowing the iron to oxidize and stain the liner. In other words, if I have a problem with iron in a pool, and I add sequestrant, am I working against myself to treat that pool for phosphates?