Is that backflush the filter? or the pond? If it is the filter, we
could use some info about it: size, kind, media, etc. If it is the
pond, most of us drain some water and add some, but it is hard for me
to grasp what backflushing it would be. People vary about how much
they change water. Phyllis have been very slow to change much.
Mostly we add. Others seem to like a lot more...they will explain to
you why that is constructive.

Jim