Ok so just for full disclosure....
Test levels as of last night... ph 7.4, TA 110, FC of 5 with a SWG. Taylor K-2005 test kit.
Seasonal pool, ongoing issues as all y'all know with metals in the water. I can't keep the water color-free for more than a few days. Water turned the color of Mountain Dew Sunday. I started getting some iron stains on/around the skimmer and return. I converted to SWG last week and got some Purple Stuff yesterday. I doubled the dosage last night. The water is better, but is still a little yellow. However, the staining is clearing up.
I talked to the folks at Jack's Magic this morning. They were the first of 4 companies to suggest that it sounds like my issue is too low a CH level. They said any sequestrant but especially theirs works better at higher CH levels, like 200 or better. Mine is 90, or was the last time I had it tested a few seasons ago. I was told back then that it didn't matter much because a) it was a vinyl pool and b) it was a seasonal one. So I haven't worried about it till now. The Jack's Magic folks differed though. They said too low a CH can eventually degrade vinyl.
Pool Calculator says I need 109 oz of calcium chloride to raise the CH to 250, assuming an initial value of 90. I will test my water today to confirm the current level. So, if I add that much, will it mess up pH or TA? I am more worried about the TA. The pH I can adjust pretty easily. Do I add it all at once or over a few days?