Algae such as Green Hair Algae, Cyanobacteria, and Dinoflagellates are all thought to become a problem when nutrients are not kept in check, or the Redfield ratio becomes unbalanced.
Green Hair Algae is known to take a foothold when phosphate increases and becomes unbalanced. Your nitrate may be maintained at a comfortable level, but as the phosphate level increases, the ratio is no longer in place. In fact, the very first thing a reefer will do is test for phosphate and add GFO, hoping that they have caught it before it takes over.
Cyanobacteria is one of those things that seem to happen for no reason, but in my experience I have had it occur twice. Both of those occasions was caused by my nitrate almost zeroing out because of rapidly growing macroalgae in my refugium. According to the Redfield ratio, my nitrate and phosphate reversed ratio.
Dinoflagellates can be caused by lack of both nitrate and phosphate in a new system, or even a lack of either one. In established systems, dinoflagellates can emerge when you have allowed your nutrients to unintentionally become unbalanced for too long. In my case, I was having a problem reading the colour chart on my phosphate test kit. I assumed everything was okay. Then I noticed my coralline algae had stopped growing…the dinoflagellates noticed too! This was another case of the unbalancing of nutrients.