Can anyone offer me some advice? I have constantly been at 0 nitrates and phosphates for months. I started getting this really gnarly algae and I've been cleaning it off my corals as it covers everything in tank, only to find the next day its covered them again. I went to LFS and he said it was cyano and told me to dose nitrate and use bio s and NP pro from Aquaforest. It's been two days of it, and still really intense stuff that's suffocating the pumps I have as well. I'm really lost for what I should be doing, or if it is even Cyano (watched videos explaining cyano is from high nitrates ???)
Here are pictures that may help illustrate what I'm experiencing.
Note, that is after a single day of it being cleaned off the surfaces.
Today I will be attempting a 20G water change in which I will try and blow up off rocks and vacuum the substrate in hopes to get as much as I can. As well continue dosing nitrate, bio s, and the other one in hopes to raise nitrate and nitrifying bacteria.
For filtration I have just a sock and a cup full of carbon, and I have chaeto in refugium with light on 6 hours a day to try and reduce its growth. I have a skimmer but I have left it off from the advice of LFS.
Would anyone have any other advice? Any and all help is appreciated

even just letting me know if I'm doing this right, as I am a noob hobbyist.
Thanks! And I'll be posting much delayed updates shortly!
Edit: Also what is maximum I be raising nitrate by at a time? Bottle says calculation is (total volume) * (# ppm nitrates I want) * .1261 = amount of ml to add.
However 315ml of this stuff is a lot to throw in all at once I'd imagine and I'm afraid it would shock them. I added in 10ml both days to increase it, and just did test and its 0.00..... lol
temp: 77
salinity: 34.1
Alk: 10.4
ca: 440
mg: 1900
nitrate/ammonia/nitrite/phosphate: all 0
I have aprox 10-12" worth of fish
I have aprox 10-15 snails, 1 urchin, 2 hermit crabs
I have finger leather coral, acro frags, monti acro frag, anemone (who has not been happy in the slightest), zoa frags, and favias. My GSP is also covered in it a lot.