I thought I would share this one. I have been a steady lurker for a while picking up many tips to maintain clear water. Lately my pump pressure has been steadily increasing and sometimes while vacuuming I would see dirty water coming back through the returns. I thought initially that my gauge must be bad and maybe a bad spider gasket but the other symptoms which include a slight decrease in flow suggested otherwise. I have three large pine trees around my pool which drop thousands of needles into the pool each season and a large labrador who loves to swim daily. His fur does clog the skimmer and pump strainer basket but this is not a big deal.
I am probably one of the few people on the planet with an old Jacuzzi Laser sand filter so I have been reluctant to perform the "deep cleaning" or inspect the valve etc for the fear of tearing a brittle gasket that I would be challenged to find.
Anyways the time has come so I took it apart. I put my hand in the sand and sure enough the top layer was a coagulated mess for the first inch or so. It had the consistency of bread dough. I scooped out this mixture of gook, dog hair and pine needles, all of which could not pass through during routine backwashing. Below this layer was nice clean sand. A quick rinse before switching to filter and the system was once again running nicely.
I tried to post a pic, but the file was too big. I am sure everyone can get a mental image of a small pile of coagulated sand mixed with hair and needles.
Something for other dog/pool owners to watch for.