[NeverlosT]

it sounds like you folks need to make a solidworks model of your pump and propeller mechanism, then perform some flowworks fluid dynamics analysis on it. From what I've read here, it looks like you are having issues modeling your predicted output since your calculations arent accounting for viscous effects of water so there is a lot of drag involved that the model doesnt account for. This would be exascerbated in smaller pumps by the more restrictive shields in perportion to the propeller size and flow.

My suggestion? Hire an engineer very familiar with fluid dynamics and you will have accurate predictions of flow quickly. Furthermore, once a model is made, it is easy to tweak the model, without having to go through costly prototyping, to determine what may help your design.

good luck! I use Tunze in my frag tank and Ecotech in the display, I like them both. I can easily recognize the problem that you are facing. Designing a high flow pump that isnt so high RPM that it will cavitate, that has enough shielding around it that it wont suck in critters, but that has enough output to satisfy a public that always wants more flow. It is tough!

what I see as your largest issue. Ecotech pumps are large but the in-tank footprint is small so they are able to make a LARGE propeller and shield mechanism without it seeming huge in the tank, since the other half is outside. Tunze must try to make a large propeller and shield mechanism with the motor integrated, which results in a larger in-tank presence that likely has detrimental effects on sales. Id suggest looking into a sealed motor where the stator is in the center and the rotor is along the outside with fins mounted directly to it, the entire thing could be shielded and your intake area could be spread all around the motor resulting in less drag and less starving of the pump. I've got some better ideas but without being on your payroll im not giving them up!

good luck!