If your phosphates are low I would recommend continuing to dose especially because you have a genus of macro that tends to like to melt and release gametes if it gets really stressed (nutrient pour environment). You may not really be at zero as hobby grade test kits can have a small standard deviation in both directions. Dino’s tend to thrive in low nutrient environment or when there is an imbalance between nitrate and phosphates. at least that’s the common thought in the hobby. I had a terrible species that no matter how well balanced my tank was, my Dino’s wouldn’t disappear so it’s not always true. Cyano will most likely come and go usually with the season. I see it happen a ton from summer to fall and spring to summer. Flow will help as the person said above. Cyano is a bacteria so there is something that it is enjoying in your environment that it’s using to grow on your macros. By the way, not sure what kind of corals you’re going to keep, but I’m using a twinstar freshwater planted tank led over my mix coral and macro tank. Has grown corals really well even sps and I enjoy the white light look. So keep fw lights in mind as their spectrum might be just as good if you’re not looking for a super blue reef light.