If you are having issues with hair algae and cyano
bacteria you need to figure the source out for those problems. The sand sifting gobies will work on the sand but usually in one specific area. They are territorial and will stick close to home. I would not suggest getting a blenny to deal with the hair algae. A reading of phosphates says that you have too much in your system. You may want to run a phosphate sponge or some other phosphate export method. Test your source water for phosphates.
What kind of food are you feeding and how much? what kind of filtration do you have in the tank?