This is my third summer with this pool and I have never seen this before. I live in AZ so we started swimming just after Easter, my pool chemistry was good. Then back in May I started getting a white dust in the pool. I don't have Jandy valves but in the skimmer basket there is a pipe from my main drain that was capped. I opened it and bought a diverter to start pulling from the main drain as well.
I left town for a few weeks and when I came back my salt had dropped from 3100 to 2800, my CYA dropped from 60 to 30 and my calcium hardness went from 350 to 490. Everything else was in the normal range. I figured there was a leak somehwere in that main drain pipe (which might have been why the PO had capped it) so I re-capped it. I put in 40lbs of salt so my SWG would work and a bit of CYA but I didn't want to load it up with chemicals in anticipation of having to do a partial drain to lower my CH.
Despite the additon of salt, over the next 2 weeks my salt dropped back down to 2800 and the CH went up to 670. I thought I still had a leak and as I was looking at the output pipe on my pump and there was a tiny trickle of water. That hardly seemed like enough of a leak to be effecting my chemistry so much but I removed the pipe and re-sealed it with Tplus2. Then to test for a leak I did the bucket test, I shut off my auto water filler on my pool and marked the level. Then I put a 5 gallon bucket filled mostly with water on my top step and marked that level. After 24 hours both the pool and the bucket lost the same amount of water, a little over 1/4 inch. So I thought I did not have a leak and my chemistry should stabilize.
I put in another 40 lbs of salt (raising me back up to 3000) but in the last 4 days I am back down to 2800 salt and my CH is at about 1000.