Looks like I'm about to buy lots of things to try to fight this. Still not quite understanding the state of the iron and ability to actually remove it. Understand once sequestrant is used it definitely can't be filtered out. Still unclear whether after using the AA and algaecide there is an opportunity to try to filter out using polyfill etc. I've read so much conflicting information today on metal staining. I guess we are going with iron (vit c spot worked) with unknown source! Even though iron shouldn't have shown up with low pH and no FC at opening, ugh.
I decided to do an AA treatment this year. I had my fill water tested, and the iron content is "ND" (not detectable), so my fill water wasn't the issue. In my case I had a rebar stain that was producing active rust from a piece of rebar too close to the surface of the plaster. I mean active like last season rust particles formed in a lump on the plaster where this rebar was and brushing it poofed off a big cloud of rust! I took too long to deal with it (multiple seasons) and trying to get someone out to fix it during pandemic times was really difficult so it was end of last season by the time someone came out for it. So by the time I took my pool water to the pool store for an iron test, the level was 0.2. I had orange stains on my white plastic fixtures in the pool - like the main drain and intakes for the waterfall etc and also brown staining on my plaster.
I have a 40K gallon pool so put two pounds of AA in, sprinkling around the edges. The miracle everyone else describes is real! The plaster and all fixtures looked brand new in short order! But I didn't want to use sequestrant because it is expensive (someone above said it wasn't, but it seems to be about $30 per quart, so $120 for me every time I would have needed to top it up!) And because I am not adding iron back via my fill water, I just wanted the iron gone from my pool water! I put polyfill (ripped out of some $2 walmart pillows) in the three skimmers I have and turned the main drain closer to closed than I normally have it to pull more water through the skimmers. After 24 hours I started raising the chlorine again fairly slowly - which was easy because the AA seemed to be eating the chlorine in a big way! The pool stayed sparkling and polyfill bright white, until about five days later when I started pushing the chlorine up higher and my ph had gone up a bit to 7.6 or so. Then over the course of an hour, my pool went from completely crystal clear to lime green - but still very clear. From that point on the polyfill in the skimmers started turning brown, and it took about 24 hours of leaving the filter on high speed, changing the polyfill a few times and keeping the chlorine around 3-4 or so to get the pool clear again. There may be some slight staining back, but certainly nothing compared to what it was! I may do another half strength AA treatment, but I'm not sure. So it's too soon to call success yet I guess, because maybe the staining will come back over the coming week or two. But so far, I am hoping I got alot of the iron out by filtering and avoided using any sequestrant.
The pictures below show
1) the pool after AA treatment
2) the pool after the one hour change to green color that happened a few days later
3) the polyfill after it had been in the skimmers overnight that same night
4) the pool after 24 hours of polyfill filtering following the lime green color change with chlorine around 3-4. It's 95% clear (that picture was taken in less light than the first one - they aren't really as different as they look). That is a watermelon ball 9 feet deep in the last picture.
