Cyanobacteria Bloom Returns?

So my 20 gal sw setup has been battling cyano for the past couple months. I have tried the meds for it but it didn't work. Best thing was shutting off the lights for a few days which killed most of it. I keep my lights on for about 16 hours per day. The fish are fine with it and used to it. It seems long but it's honestly the only light in my room because my ceiling light is different sized and it is a pain to find different ones, lol. Anyways, I am finding more cyano. I will siphon what I find out or shut off the lights a couple of days. I found the source turns out to be from the tap that I use to top off the tank after evaporation in between water changes. I did a test and the tap has about 1ppm of phosphorus, which is not perfect. So the tank is at about .5ppm of phosphorus. That is VERY high. But no matter what I do, the cyano comes back which is irritating. I also have some type of green algae that I think may be hair algae starting to form. I am focusing on my bettas right now but I do plan on starting up soft corals and possibly macro algaes in my sw within the next several months. Would these plants help me with my cyano issues and possibly the hair algae? My juvenile maroon clown will pick at it sometimes but she doesn't do anything, and the juvenile green chromis ignores it entirely. My zombie snails (for lack of being able to spell their actual name, lol) obviously just eat the excess food that the fish miss so they are of no use algae wise. -I know my clown will have to be moved. She will be changed to a 50 when she outgrows this one. She isn't growing particularly quickly and is only about an inch and a half or so.-