Sand in pool from filter

[smerel]

Hi, I know it is a reccuring question, but I did not found my answer in any previous person having this problem.

I had sand in my pool and changed it because it was old (10 years) and started looking pretty brown and small. I tought it was the size that made it go throug the laterals. I inspected the lateral and found the bottom cracked, so I bought a new one and replaced the sand with new one made for pool filter.
My water is much more clear now, but I still have sand coming back to the pool right under the jet. Obviously, its the new sand. When I replaced the standpipe/lateral/sand I was very carefull so im pretty sure it's not broken. the sand goes just under 3/4 of the filter.

Now I have theories but I need advice from you guys as you are experts and its my first year I own a pool.

First theory : psi is around 15, it was around 10 before changing sand. maybe the pressure is too strong?
Second : the sand is too small for the laterals and pass through, it is quite big grain actually, so I doubt it's that.
Third : Im not sure the standpipe and the head gasket is well aligned with each others, I don't know how to check or how to be sure it "fits" when you replate the head gasket to the filter.

Thanks for your help!

 

[pooldv]

Welcome to TFP!

If your filter is putting sand in the pool then something is wrong. 15 psi is not anywhere near too much. Are you rinsing? Review these procedures to see opinion you are missing something.
Pool School - Maintenance and Cleaning of Pool Filters
Deep Cleaning a Sand Filter

 

[smerel]

Thanks, interesting posts. I do understand the multiport position and did a long backwash/rinse after changing the sand. There was no ´dust' coming back to the pool when i put it back to ´filter'. It took a couple days before i noticed big sand grain in the pool. It slowly accumulates so it is not residue from pooring the new sand into the filter (the standpipe was blocked by a cloth). Something else i noticed was that i cleaned the pool on rinse to put back the sand into the filter and some small leaves particules i sucked came back from the jet but only a very small portion. Thoses particules would have been filtered so it somewhat bypassed the standpipe and the laterals. I wonder if it is the same problem that causes the sand leak?