Find out how to calculate head pressure and properly size your return for a saltwater reef aquarium.
www.bulkreefsupply.com
Based,on that article, Aquarium size x5-10 so the s2 rated at 1400 gph would fit the bill, but you will need to run it at higher rate to meet the 10x turnover, less so for 5x. But dburrs suggestion is a good one to go bigger and run it turn it down to put less wear and tear on the pump.
Or better yet, get a second s2 and split the load by going dual return pumps, plus that way you have a redundant return pump for when one inevitably fails. <~ this is what I’m doing…