I have been struggling to resolve a problem w/ DE constantly appearing in the pool. I've replaced DE filter screens (twice), replaced spider gasket, cleaned and lubed the multiport valve. I have an American Titan 36sf DE filter and 2hp circulation pump.
Saturday, I replaced bearings in my circulation pump motor and disassembled the pump. I cracked the pump/motor seal and allowed water to drain to ground. I did not reset mulitport valve. When I pulled the motor and impellor out of the pump housing, I noticed a good amount of DE in the bottom of the pump housing and impellor. Could this be the source of my persistent DE in the pool? My thought was that somehow the multiport valve is allowing the DE filter to drain back into the pump casing on shutdown(filter is higher than pump). It would seem there would have to be a leak path (to drain?) through the multiport valve for the water to flow backward when shutdown. I have not noticed any leaks.
This has been going on for 1-2 yrs w/o resolution.