this is to be saltwater?
I am not sure if most people on these forums realise, but x7 turnover for a small saltwater tank is WAY too low for flow.
I dont know how much your overflow can handle, but I would look into getting the biggest overflow you can get on this tank.
you need atleast x30 turnover, which is around 700-900gph flow, which means you need a high head rated pump that does around 1000gph, there are some blueline and other pumps that do that. is of course is provided you can find an overflow that would allow for such a flow - doubt you could with a hang-on-back one.
with saltwater, dont skimp on flow, you will still need to add more later via powerheads, which will take up alot of room in such a small tank and look ugly. better plan it form the start.
Saltwater is eventually expensive, even for smaller tanks, plan ahead.