Diatomatic algae blooms are normal in new tanks. If this is not a new tank, there must be a source of silicates in the tank. Is your sand aragonite? I assume you are having a cyano outbreak? I used blue vet red slime control with great results. I mixed it well in a cup of sw first, and running your skimmer is impossible during treatment. A Phosban works great, the directions tell you to remove it after 4 days. By then, if you dose correctly, you should be at 0 Phosphates. I just use a filter sock and place it in my sump above the return. You could however run a reactor with some ROWAphos, and some carbon, but to me, that's more work than I want. You would need to pull and change your media often. If you are buying water, test it before you add salt. You may just be dumping phosphates into your tank.