Zero- if you would like to measure the flow in your tank. Here's how you do it:
Calculate the total flow of all of your powerheads within your display. Then add the volume of the return (I'm not totally familiar with how your tank is set up). These two numbers together would add up to make your "flow" within your tank.
However, "turnover" is the volume of water that's passing through your
sump. This should be the volume of your return pump.
Many of us try to aim for 15-20X the volume of the tank for the "flow" within the display. You want to have your "turnover" much less, around 5X or so, so that your
skimmer can be as efficient as possible.
Hope that helped....
