Re: White flakes in water
Most likly calcium. When your salt cell reverses polarity to 'clean' itself the calcium that had formed on one set of plates is released into the water. It is usually a good indication that you are letting your pH climb too high, which will lead to precipitation of calcium carbonate givin your high calcium levels.
My suggestion would be to bump your CYA up to 80 ppm and lower your TA to about 70 ppm. You might also want to consider adding borax to 50 ppm to your water to act as a secondary pH buffer. This has been found to be extremely useful with SWGS. I would also lower your output a bit so the FC is closer to 4-5 ppm. 7 ppm is overkill and just means the cell is on more than it needs to be. This leads to a faster pH rise which causes the calcium precipitation.
Done together the above suggestions will have the effect of causing less outgassing of CO2,which means your pH will not rise as quickly, which means you will be less likely to precipitate out calcium carbonate.
Also, you will find that you will not need to add 3 cups of acid weekly.
Once you make these adjustments keep the pH at 7.6 and not lower (lower pH causes faster outgassing and faster pH rise) and when the pH climbs to 7.8 add just enough acid to lower it ot 7.6 and not lower (this is where an acid demand test is very useful.)
The why behind my suggestions has been discussed at length on a different pool forum that I am no longer associated with because of 'new management' but that I was a moderator of since it's inception up until I left shortly after the management change.
Bottom line, my suggestions are the key to a salt water pool that is basically "trouble free".
11.75'x23.75' kidney 6.5K gal IG fiberglass pool/300 gal acrylic spillover spa combo; Aqualogic automation/SWCG; Pentair Clean and Clear 150 cart filter; 1.5 hp uprated 2 spd Pentair Whisperflo pump; PF:17
Retired pool store and commercial pool maintenance guy.