On 10 Oct 2004 22:13:48 -0700, (Rob) wrote:

I've got an Oase Filtoclear 800 for my small (400 gallon) pond.

The question: When should I do this, and how often?

Never had one of these for a pond, but pool pumps are similar backflow
cleaning units. You can evaluate the output flow and fluch when is is
reduced. A better way is to put a pressure gauge on the output and
flush when it climbs.
You will flush the crud, but enough active bacteria will stay on the
grid.
--
Crashj