Since his filter is a TT type, the pump does not come into play for draining
purpose. However, your explanation still apply to the drain from the filter.
Draining should be slower because it take energy to move the water at the outlet.
t's only gravity flow from the bottom of the filter into the pond. He should open
his filter and see how much water back up on the bottom. If water back up 1/4 of his
TT, then he should be concerned about drain flow.



george wrote:

It will have an affect (even if only slightly, at the depth), because it is
placing a hydrostatic head on the pump that it has to overcome. Most pumps have
charts that come with them in the manual that tell you what the rated output is
for a given amount of head. At that depth, it should not have too great an
affect on the pump