<a href=showthread.php?s=&postid=7010477#post7010477 target=_blank>Originally posted</a> by Treg
To me, Turnover rate and maximizing your overflow are 2 different things...
I definitely agree! Although, sometimes it's overlooked...
IMO, tank circulation is simply increasing the current in the main display to provide more water movement and increase gas exchange. System turnover is how much water is being exchanged between your main display and the area(s) of filtration (primarily a sump with a skimmer and/or refugium). It is important to separate tank circulation from system turnover, primarily for the latter reason:
The surface of the water contains the highest concentration of protein-rich material, which gets skimmed off via the overflow. In a typical Berlin-style setup, this water flows down to a sump where it immediately hits the protein skimmer. So, you first want to make sure the tank's drain-line is located very close to the skimmer's intake; otherwise all of the tank's surface skim rises back up to the sump's surface and likely ends up getting pumped back up to the display tank. Secondly, you want to try and match the flow rate between the drain line and the skimmer's intake in order to optimize the skimmer's functionality.
Now, if you want to increase the circulation of your main display, my advice would be not to add on another return pump or buy a bigger one. Also, a standard RR AGA has a 1" bulkhead and, to my knowledge, it is not physically possible to drain more than 600 gph through it (unless you're creating a siphon). Your two best options for increasing tank circulation is building a closed-loop, or adding on PHs or stream pumps. IMO, the latter option is best b/c it allows for more indirect current, which, depending on your selections, can even be variable (e.g. TUNZEs on a multicontroller or a CL w/ an OM).
~Aaron