Looks like chunks of plaster from a slob getting some into open pipes during construction. You're very lucky they came loose and came through without clogging a pipe somewhere underground. If any of your returns look weak, you know what to look for now. People are always finding bits of stray plaster behind the eyeballs.
I built 2 pools by 2 different pool builders in the last 5 years. In the neighborhood of 1 year in, I found similar things in my filter baskets. I never could find out where they came from, especially in my current pool where the plaster is blue and the "rocks" were white.
Hello , This thread has been inactive for over 60 days. New postings here are unlikely to be seen or responded to by other members. For better visibility, consider Starting A New Thread.
Welcome to TFP! For a wealth of pool care information please check out our free Pool School. If you are in need of specific help then we encourage you to Register and ask us here in the forum!