BigTallDumbGuy was referring to waterbear's post where he wrote "When CYA levels are very hiigh for an extended period of time CYA tends to deposit in the plumbimg and pool surfaces and when you refill it residdolves and brings the level higher than you expect." I have heard that before in the context of there being a small amount of residual CYA reading in spite of pools being drained. However, 4 pounds of CYA in 11,000 gallons is 44 ppm and that's much higher than the kind of residual that can be left over. Since a proper test kit was never used in the pool being described that had CYA in it, I don't think it's worth spending any time trying to figure it out.