I get pest algae’s and Cyano when my nitrate to phosphate ratio is not balanced.
When I correct the imbalance they just go away on their own. About 2-3 weeks after correction.
I run phosphates at 1/10th nitrates. Not exact, but close and stable.
My nitrates run 5ppm and phosphates 0.05ppm.
Last time I got pest algae and Cyano, nitrates were 25ppm and phosphate 0.01ppm.
I dose carbon not to lower nitrates but to increase the good algae populations which in turn eat the phosphates which in turn are consumed by corals. Corals can take in nitrates easily, but phosphate, not so much, but they can take in the bacteria which contains the phosphate.