0.4 ppm is fine for some SPS. In fact some tolerate even higher phosphate. My large anacropora here grows like a weed with great color and my phosphate problem was much worse than yours (2.0 ppm). My acros browned out though and are just starting to color back up at 0.2 ppm. I’m aiming for 0.1. If you don’t have a desire to keep acros, 0.5 ppm is probably fine based on my experience.Wait do you got sps thriving with nice colors at 0.4 phosphate? What are you nitrates and how are you delivering them. And how do your phosphate sit higher do you feed a coral food or fish food that is boosting it or nori or are you dosing? Just curious