I've found water changes to still be very helpful, the corals just do better imo after the water change. I do about 30 gallons in a 120 total water volume every 2 weeks or so. But I run carbon as well, so part of it is just nutrient dilution since I feed pellets 4x a day and frozen at least once. Heavy nutrients in, heavy nutrients out and I struggle to keep phosphates detectable at all. I probably have more nuisance algae than I'd like, but nothing a little elbow grease can't take care of. I think if you were to do some icp testing you could look at lowering the water change frequency, but I'm still not comfortable pulling the plug on that routine.