As a general rule, an external pump should have some sort of strainer basket. When I had 6 Koi ponds, the only external pump that burned out on me was the only one without a strainer. And all of them followed a gravity fed settlemt chamber, vortex, or biofilter.
The one that did burn up was a Grunfos recirculating pump. Admittedly not often used for Koi ponds. But it drew very little amps and moved a lot of water! What killed it was little more than a small bit of string algea. Those pumps were made for clean water.
Unless whatever section your pump is drawing from is always covered, there's always be a chance of something getting in and heading for the pump.
Guess that's why so many external pumps are bundled with an intake strainer. If not, they usualy tell you which one can be added to the pump.
I just think having one is a good idea.
Mike S.
Spring Hill, FL
