It did take a few days to a week for me to really disapear and at the same time I improved the water quality by syphoning the sand and doing partial water change.

Cyano is not so much about phosphates, nitrates or light, but more about dissolved nutriment in the water and sand. That is why an oxydizer like Red Slime Remover might work if your dissolve organic load is high. Hard to mesure that as it's not the same thing as nitrates or phosphates.

I would wait a few days to see if it improve more and redose if it's not all gone. If your organic load is very high you might need a few treatment to make it disapear completely.