I have a Hayward S220T sand filter. After my first vacuuming of the year to get up all the black dirt/silt at the bottom an hour later it looked like most of it returned. When I do the first vacuuming I usually need to backwash 2-3 times to keep up the suction. My Filter normally runs at about 20psi (which I think is high, but may be due to poor DIY plumbing from the previous homeowner) and I normally backwash every 2-weeks when I re-fill my chlorinator regardless of pressure.
I backwash into the ditch in a corner of my backyard and I noticed a bit of sand collecting there. It looks like sand is coming out when I backwash, not rinse, so I don't think it is a lateral issue. Also, I don't see much sand in the pool, just fine black silt/dirt.
I have had two different pool people out. One wants to change my sand with zeo sand and check to ensure my multiport is not broken. Another guy said he would just check the multiport and top off the sand if needed. He also said I could do an acid treatment to rough up the sand.
I can't open it up myself for the deep cleaning as there are no unions, I would need to cut all of the pipes. Whoever I have service it I am going to have them put in unions. I already tried a long backwash (4:00 minutes) per what I read here about possible grooves.
Sand and filter are 5+ years old and pre-date me purchasing my house. I would welcome any suggested next steps...Thanks!