[Help] Cyano god strand?

Soooo Ive had a Green hair algae problem in my tank due to phosphates (Im new) I started using GFOS and rigorous siphon cycle. Im now at <0.03 ppm but now I have a Cyano problem? Started coming about after I got rid of the algae.

The weirdest part is, its growing on the sand right where my powerhead hits, so its not a flow issue. I dont have phosphates that would cause this, I use DI water, My light used to be on a 12 hour cycle (Yea I know kill me) Its been on a 8 hour cycle for about a week now. And Ive tried manually removing it a few times now to no avail.

Im not one for chemicals but I thought Id try Chemiclean, its now hitting the 48 hour mark, the time it says to run it for then do a water change, but it hasnt even stunted the growth at all. I did everything it said to the mark.

I dont really know what to do next, I heard since its a bacteria it doesnt feed on phosphates so I have no clue what the heck im supposed to do.

Mind you the tank is hitting the 6 month mark.

Update: I just did my water change after the 48 hours as stated by the Chemiclean. Did a water test heres the parameters.

Before Chemiclean: Ammonia 0.1ppm Nitrite:0 ppm Nitrate: 2.5 Phosphate:0ppm Calc:400ppm Salinity: 1.024 PH:8 Temp:78F

After 48Hours

Ammonia:0.1ppm Nitrite: 0 Nitrate: 5ppm Phosphate: 0 Calc: 450 Salinity: 1.022 PH: 8 Temp:79F