If adding DE to a sand filter, how long should it stay in there? Just til the next backwash is needed? How soon can I start vacuuming to the filter after adding DE to the sand filter?

Right now my filter just blows all the silt back into the pool thru the return line, does this mean that the silt is too fine or that there's something really wrong with the filter. Just curious so that i don't dump DE straight into the pool.

Thanks in advance.

tc