What type of filter?

Noticed my sand filter shooting some debris through the returns this year. After 9 seasons with the same sand I decided to open up the filter and take a look at it, turns out I was missing some (actually, a LOT...it turns out the laterals were never installed flat, so a little bit of sand was shooting through a few of them....a little bit at a time over 9 seasons adds up).

Changed the sand and filled back to normal level and I no longer get anything shooting through during vacuuming.