FAC=2
pH 7.4
Calcium Hardness=500
([Leslie's] stopped the rest of the testing and dumped the water out after he asked me if I was going to drain and refill the pool, and I said "yes")
Well, I don't think they did you any favors here! :lol: Wonder why they thought that the rest of the numbers wouldn't make a difference in how you treat your water (despite the fact that you're planning to drain?) The pH, as you probably know already, is OK. The Calcium Hardness is high, so that suggests that your pool water is already saturated with calcium. It would be nice (for you) to know the other numbers: Combined Chlorine (CC), Total Alkalinity (TA) and Cyanuric Acid (CYA). Leslie's may or may not be a reliable source for these. Perhaps you should consider getting your own test kit prior to opening in the spring so you can test the water in your newly drained/filled pool.
Pool water is about 4 years old and 55 degrees, if that makes any difference....
I'd also like to note that a well-meaning friend who says he used to work in a pool service company acid-washed our spa early last summer. The plaster is about 6 years old, and he used pure acid to do the wash, then rinsed it off as I watched. For the next several months, the white plaster in the spa kept flaking off and finally stopped flaking off a couple of weeks ago.
I don't know if that would have anything to do with the flakes now coming out of the pipes. I never had these flakes coming out of the pipes om the spa until a couple of months ago. I wonder if what is coming out now (only when the heater is on) is residual?
I've never acid-washed my own pool and can't assess whether this was the proper method (other members may have something to say to this) but since you report a recent history of flaking, perhaps what you see now is indeed residual from the acid wash.
The size of the yellowish flakes vary from a little larger than a grain of sand to about 1/4"-3/8" in diameter.