after back wash de in the pool

[mj]

after the back wash I got de from the filter in the pool.I can not understand why. what could be the disposable reasons?

[mr_clean]

after the back wash I got de from the filter in the pool.I can not understand why. what could be the disposable reasons?

you could have grid that has a hole in it so DE leaks back into pool when pump is on.
Where does the filter dispose of DE when backwashing? Some go to backwash trap that goes to sewer, some go into garden & some have backwash tank that catches it in a bag & that could be leaking if you have that system.