I have been a vinyl pool owner for 3 years now, and each year I have tried to tackle a balancing issue. Last year I tackled CYA (I had near 0 and was losing FC rapidly during the day). I used a conditioner to increase CYA to about 50-60, and FC problem solved.
This year, I am tackling calcium hardness. CH has always tested at about 40ppm using my Taylor K-2006 kit. Yesterday, I broadcast about 25lbs of "Pool Mate Calcium Increase for Swimming Pools" (made by Robelle). It all dissolved very quickly, no cloudiness or white residue. Immediately prior, I tested FC at about 3.0 ppm.
Good news this morning is CH is testing at a much more reasonable 240 ppm. Bad news is FC is down to 0.6 ppm!!
I have an SWG (Pentair IC-40) that I generally run at about 40% capacity 24/7 during the summer (next year's project is getting off 24/7!). I checked CYA again this morning and it is around 60ppm, so that's not the culprit for the FC loss. I don't see any algae or organic growth. I jacked up the SWG to 70% output about 3 hours ago, and as of yet, no change in FC.
My question is: Can adding 25lbs of calcium chloride at once have a short term impact on FC?
Alternatively, could my SWG be going (I probably have over 10,000 hours on it and have never acid washed)?