CYA coming back through returns?

[rmeden]

Normally the backwash valve is considered separate from the filter (right before and after it). Maybe yours appears as a single unit.

I think you're right.. CYA is bigger than DE... if you didn't add enough DE it would still be caught by the grids.

I think you'll need to open your filter and check the grids for tears.

BTW, CYA disolves slowly... it normally is caught by the filter and disolves from there. If the CYA gets through, your filter isn't filtering.

Robert