Yes it is a sand filter.
I'm not sur ethe brand or name of the filter aid, but the pool was cloudy and the filter was running 24/7 for a week and it was not clearing up much.
I had the water tested and had added the proper chemistry up on opening the pool to adjust PH, calium hardness shock etc.
They suggested the filter aid to help the filter do a better job filtering and catching the smaller particles , maybe precipatied calcium.

I added it and the poolo was crystal clear in about 3 days.

Everything was fine for a couple weeks and then the filter flow decrteased and the time between backwashes got shorter and shorter to restore the original flow.

So I'm just thinking that stuff has clogged the top end of the filter or something like that .

I was just wondering if anybody knew of anything I might use to backwash it with chemically to dissolve that stuff out of the sand and restore the flow if possible, short of replaceing the sand altogether.

Like i said , the filter is essentially new, only a season and a half of use to date. And last year I did a complete filter cleaning sequence. Draining and running filter cleaner thru etc.