White sand in a earth filtered pool

[E.Collins828]

I have a gritty white sand like residue on the bottom of my pool. (Unground 18x36 DE filter) it feels like and looks like white sand, not earth. There is no pressure change in the pump, the water is clear, and smells of chlorine. Wife says it’s earth and believes it. So unless I have a hole in some of the flex tubing, which there isn’t one, if it is earth, how is it getting through the filter side of the tank? Also I work at a place that uses a lot of chemicals and 1000’s of gallons of bleach a day, we test for sodium phosphate and sodium carbonate. I’m convinced it is one of these two and not earth. What test kits should I get other than ph, chlorine and the useless sticks to check these levels?

[Denniswiseman]

It won't be earth as you would need a leak and then the water pressure coming out would stop it coming in

[mknmike]

Could it be sand from the pool plaster? Maybe an acidic ph is deteriorating the plaster pool liner? Could that be?