Hey Minh
What I mean is that typically, the hole that runs parallel to the run of the impeller shaft is the intake and the exaust is perpendicular to the impeller shaft. These pumps are just the opposite. They draw water in from the vents on the side and pump it out the hole that runs parallel to the impeller shaft.
This design would have worked well with the previous design of our DIY calcium reactor. It doesn't work well with the current design. Although, if the pump was at the bottom of the reactor, under the media, this pump would work. You got me thinking.
I'll bet that impreller is more plankton friendly that the traditional design.