I should have done a Google search before posting! Looks like mentioning 'ionizer' on a pool forum is akin to shouting 'democrat!' at a republican party (or vise versa!). I've had my inground, 28000 gal pool for 14 years. The installer convinced me to build it with the ionizer (to save $$ on chemicals) and I have to say the pool's chemistry was pretty much perfect up until last year (I would add a gallon of bleach every 2-3 weeks). Last year the pool started losing water via a small hole and until I figured that out I kept filling it with well water - which of course is loaded with minerals. So the liner started looking stained. I added Stain Free and it seemed to clear it up, however, I opened the pool about a month ago and the shallow end looks stained to me again. So I was just looking for info. I think I'm going to hit it with ascorbic acid & another Stain Free treatment, back off/shut off the ionizer, go with chlorine tablets and see what happens. I'm starting to think CONDO?