not sure on gph yet but here is a small review I found about it
"Every filter manufacturer likes to claim that their product is the most innovative, and that it filters your tank water better than any other filter. The actual truth is that most filters do about the same job as far as filtering you water goes. They are barely separated at all, but that minute separation leads to many hours of "discussion" in the aquarium hobby. What is generally agreed upon is that the bigger the filter is, the better it will clean out your water.
This month I’m reviewing an interesting filter. It’s the Sandman. This filter was designed to add the power of a fluidized bed to the normal power filter. Fluidized beds allow for a lot of surface area in a small space and thus are very useful as a bacteria-breeding area. They can greatly increase your tanks holding capacity and are generally sought after. So the Wardley Sandman was an interesting idea, unfortunately, it didn’t work as well as they would have liked. (SandMan ES, LS, and MS rec. for 10-38gal, 30-75 gal and 05-15 gal respectively)'