Swapping out the water like that works really well for my dad's 80 gallon SW tank. He's had it up and running beautifully for 20+ years. The new ocean water totally keeps the fish healthy (both store bought and caught), the seems much more vibrant and stable. He only swaps out like 15 gallons of it once per month, just goes to the beach on a clear day
Good luck with your tank! That seahorse is neat!