Back story. I just bought a house with a pool at the end of June, and previous owner only used trichlor tabs and shocked weekly to keep algae at bay as he only ran FC of ~2 - 2.5. It wasn't used heavily, and with automatic, dark pool cover, he didn't have any major issues. I got the good TF-100 test kit in July, and the CYA is ~130 - 140 (using double and triple dilution), so a water change is warranted, probably next spring. I also need to deal with iron staining in the fiberglass pool as he used straight well water at 5 PPM iron to top it up this spring. He admits this was a mistake, as now there's some streaking in several areas from the iron. Plan is to deal with it using AA this fall after the water is < 60 and letting FC drop to 0 as it cools down so the AA works. Plan is to use polyquat 60 to prevent algae growth over the winter.
I've always had high TA, typically 200 - 220, and best I've managed was to get it down to 180 one time with several gallons of MA, but it went right back up with a refill. Yesterday I finally tested the well water, and the TA is 450 on the hard, high iron side and 500 - 550 after it goes through the softener, so now I know why it's always high, and it went back up so fast after I topped it off after draining about 10" out of it and refilling. The softened well water is ~7.1 - 7.2 PH, so the high TA doesn't seem to have a major effect on this reading, at least as raw water.
I don't have a problem maintaining PH, and it seems to hold steady where ever I leave it for several weeks at ~7.2 - 7.3 right now, so the high TA doesn't seem to cause any drifting issues. My reading indicates that primary reason for lowering the TA is that PH will tend to constantly drift upward, but it doesn't seem to be an issue with the TA I currently have. In fact, I used about 3 gallons of MA to get it down somewhat, and aerated the dickens out of it for about 4 - 5 days a month ago by running the pump 24/7, and the PH wouldn't come back up with the aeration. The MA dropped the PH to ~6.9 and the only way I could get it back up was with Borax. I made PVC return aerator as pictured on here by someone else to spray the water and left the cover open. All it did was turn the water foamy and collect lots of debris and leaves that I don't normally get, but the PH did not come up with days of aeration, so I gave up and used Borax to bring the PH back up to where it should be, and it seems to stay there very well and doesn't drift up, at least not quickly.
I was going to drain and refill with soft well water next spring as needed to get my CYA down, but now I'm not sure if that's a good idea, given the extreme TA readings. Given these values, there really doesn't seem like there's any practical way to ever get and keep the TA down at the recommended levels, as it would take extreme amounts of MA to bring it down. And I suspect, it would be a struggle to keep it there given it would increase again any time water is added. Of course, this would mostly be in the spring when opening the pool, as there's not much need to add water otherwise.
The question is, how critical is it to control the TA and keep it down as much as possible? It seems that the only way I could get and keep it down is to have replacement water hauled in, and I have no idea what that would cost, but expect it would be rather expensive.
What would the experts suggest? I've read where some people have had the CYA drop significantly over the winter, but seems the consensus is that it was either bacteria or dilution that caused this, and hoping for bacteria to lower it probably brings it own potential set of problems. If I drain and replace ~70% of the water, the TA will go way up, probably ~400 - ~450 if I use soft well water. Is this going to cause problems, or what are the recommendations? It would take an exorbitant amount of MA to try to bring this down to say 120, and I expect it would be a constant battle trying to keep it there.
And I guess adding melamine to the water to coagulate the CYA and then filtering or dumping it isn't a good idea either, and might require completely draining the pool from the mess it could cause. I've considered it, but after reading some more, decided I shouldn't try it.
I'm a bit stumped as to the best course of action at this point. Right now FC = 11, CC ~0.25, CH 200, PH = ~7.3 and TA = 220. Suggestions?