right now we have 1 Sequence SW 4300 that runs our return manifold (current display tank, prop tank, chiller, calcium reactor and fluidized bed reactor, currently running GAC and PhosAR). When we switch over the prop tank will be incorporated into the sump and the chiller will be run off of it's own pump (for reasons specific to the design of the Eco Cooler cooler/shiller line). So the current display GPH + the chiller and prop tank GPH will reclaim more than enough GPH off of the manifold to run the new tank. Since we are looking at roughly 5x turnover through the sump/tank, that is less than 2000 gph. Even when throwing the calcium reactor and a fluidized bed reactor or two, @ 4' head height we might could get away with just using a Dart (and saving a bit more on the electric bill) Dart @4' is 2820 GPH, our current 4300 is 3900 GPH @4'. To that end we pucked up a used Dart to try out after we get the new setup plumbed and running (since we use true union valves and 2" spa-flex and the wet ends are likely pretty close, we should be able to swap them out in short order to try out the Dart for a day or so). We are going to be relying on the 4 Vortecs to provide the overall flow/turnover within the tank. The 2k GPH or so worth of flow that the return will be providing should be a drop in the bucket compared to the Vortecs. In our current display tank the return pump plays a large role in the overall flow, which is why we needed so much more GPH for it's return and why I don't believe that we will need as much for the new tank, even though it is bigger.