Yeah so I have basically no coral and might give Chemiclean a try, I haven't used it yet. I also put in a UV a while ago and it did nothing.Your mixed salt water is going to show TDS somewhere between 300 and ERROR in most TDS meters... Salt is a dissolved solid after all.
And green cyano too! Kinda neat. Usually that stuff is red.
There's lots of good advice in this thread but, you really can't starve out cyano. Even after you've fixed all the problems causing it to grow in the first place, it can be near impossible to kill it. A blackout won't work if you've got coral - the coral will die first; and ambient light from the room is enough to grow this stuff. It's a very resilient and efficient organism. So that said, you really needn't be afraid of a chemical solution. You still need to do the right things to keep it gone but something like Chemiclean will kill it (but will take multiple treatments) and you don't seem to have anything that would be sensitive to it. Peroxide doesn't seem to do anything to cyano. High flow will stop it from attaching to the substrate and forming mats, which in theory lets something like a UV sterilizer kill it - but I've got a ton of the red variety in my little tank and it has survived all attempts to kill it save chemical; the tank is all zoas and anemones and thus is kept incredibly dirty and I'm not willing to risk the BTAs with chemiclean so I live with it.