I have an inground 17,000 gallon pool, with a canister type filter that contains 4 cartridges (cartridge number 460, I think). The other day, I drained the filter, and all the water was chaulky white. I unsealed the filter and removed the cartridges. They were full of a white, chaulky substance that resembled extremely wet mortar. This is a first in my three years of owning the pool. Usually, the filters are just "dirty", with dirt, trapped bugs, grass clippings, etc. I can't imagine what the white substance was -- I even took a pressure washer to the filters and it took a good hour to clean the cartridges with the pressure washer. Any idea what could have caused this?
As for sterilizing the pool, we use the in-chlorinator pucks (about 3 a week, given Houston weather) along with Zappit; I put about a cup of Zappit in the pool every other day. Could that be the cause? Too much chlorine trapped in the cartridges? If that's not it, I don't know what is, since there is no construction around here which would blow dry cement powder or mortar into the pool.
Thanks for any ideas.