Pre and post Sand Change, still losing water flow

[paksoyk]

Hi All,
The problem: I have been unable to clear up my pool this season. My pool guy recommended a sand change b/c he thought the sand was bad and hence preventing good flow of water and not filtering pool water. I thought so too after replacing the pressure gauge and noticing that the pressure would go from ~12 psi to ~18 or 19 psi after a few days or in the same day, after backwashing and rinsing. When the pressure goes up, you can see that the jet that pushes the water back into the pool is moving much less water. But, it never stops completely. I inherited this pool when we bought a house in 2013 and it's never worked very well.
The problem existed last season and the one before but not as bad. Ie, when vacuuming the pool, I'd have to stop, backwash and rinse, re-sink the hose many many times to complete the vacuuming process. But, I was able to get the water clear. Water movement has also always slowed at a speed that varies.
So far the salt cell has been cleaned, maybe 2 weeks ago, and I changed the sand two days ago. But still the same problem. Current variables: 1) there is probably a fair amount of leaves and debris in the pool that came off the pool cover at pool opening in May. I haven't tried vacuuming it up b/c I can't see it anymore. 2) I hear a hissing noise coming from either the Sand filter around the multiport valve or the chlorine tablet, uhh, holder/dispenser thingy. 3) I'm not sure how the chlorine tablet holder works and have never used it. Also don't know if it's in the on or off position. When Removing Multiport valve, used this part for grip. It is now loose enough to rotate around with some strength applied. You might could pull it off w/o unscrewing things. 4) SWG feeds into something in the skimmer (have not removed the cover to look) and dispenses water via fountain. I am leaving this fountain closed to keep as much water moving as possible through the main jet.
Equipment: Intex 24-26' X 4' above ground pool; Clearwater High Rate 22" Sand Filter; Intex Krystal Clear SWG; Chlorine Tablet Holder Thingy (also Waterway? proprietary fittings); Skimmer w/water fountain

I don't have pictures but could easily go home and take some. I'm getting pretty desperate here and have on more than one occasion considered getting rid of all of it. Any ideas or input would be so very appreciated.

Thank you,
Kerry

[Denniswiseman]

Have you checked your pump for a blockage inside and good flow
When you back wash do you get a good out flow
You could be sucking in air through your pump strainer basket O ring (this would make vacuuming difficult)
Have you tried to set the MPV to recirculate and not filter to test whether it is the filter
Try and test various parts of the circuit to determine where the fault lies