Ha, cyno and dino thrive in low nutrient conditions? So if there's algae for high nutrients and algae for low nutrients, why even bother doing water changes? Sure I have algae but it's hair algae that hopefully my clean up crew can manage.
I hate the idea of a blackout, especially with coral. And what is even the problem really? Cynos and dinos? It's just algae. Is it really that bad? Of course my solution is always more (and better) clean up crew.
Algae, including protists (dinoflagellates are one type of protist) consume po4 and no3. They are heliotropic and mixotropic depending on strain. So depending on available nitrogen will also use light and spear/consume prey.
So actual high or detectable levels of ammonia, nitrate or phosphate wont rid dinoflagellates or help with algae problems.
So these nutrients as ill refer to them now on will cause algae blooms. We all know this and aim to keep them low.
As a hobby we were very good at doing this with algae (macro) and for the most part dinos were exception rather than rule.
The past five years has seen many products used to decimate organics and nutrients. Why? Because the hobby and people on here and other forums were saying we need certain levels for a successful aquarium. So carbon dosing became a thing. Its supply and demand after all. Driven by requirement. No nitrate and reduced phosphate.
Low levels cause dinos to emerge. The current thought on this is that your starving other organisms that outcompete or even consume dinos.
Nothing to do with levels though it could incite a flight or fight response. (Different strains emerge for different reasons, ie disturbed sand beds, warm weather increasing ambient temp, changes to light cycle, availability of amino acids (crack to dinos)). List goes on.
So yes, water changes help. Dilute toxins produced by protists and give corals a breather.
Low nutrients will solve algae issues but can result in protists taking over.
My advice remains the same. I've battled them for ten years before finding wins.