This is actually a very difficult question to answer. And the amount of info needed and equations one would have to run is, well, quite... on the side of head hurt.
That said, assuming you did a bit of research, and have an adequate solids filter and bio-filter. I would suggest at a minimum of four exchanges of water per hour.
Remember... You can pump all the water you want, and without reasonable filtration, it won't matter.
Sorry about that, I hope it didn't sound mean.
The shower drains work really well (I posted this type of info on another DG) 2" PVC is a definite plus. What I did is replaced the ss stamped grate with a ss filter screen. First ones were too fine, but anything like the size mesh of a window screen works. Keep in mind that they have to be cleaned on a regular basis, and a garden hose with an appropriate nozzle works on the larger mesh -vs- a pressure washer on the finer, but that is another story.
If there is a bait fish afterlife, I am sure to be on the list of those seeking revenge.
