sand filter problem.

I have a nicely sized sandfilter, 2 inch tubing, 1.5 inch hp motor and a 17000 gallon inground pool. I installed the filter last year myself (replaced a cartridge filter) and filled the filter with the zeobrite/zeosand (can't remember exactly which) sand. I used half the required amount for normal sand , as directed by the instructions for zeo. The filter is a hayward filter, the switch and piping connect on top.
Here is the problem; Every time the pump switches on for its 8 hour run, I see a puff of cloudy water coming out of the returns into the pool. It is only briefly. It seems to disappear almost right away but the water is a bit cloudy after this until the pump has run for a while.
It started doing this after I changed the filter so that makes me think it's something with the filter.
any clue why ? The new filter was installed months ago and has been backwashed several times so I would think any impurities in the sand are now gone.
and yes, I do use Rinse after backwashing.
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