Like plants, Algae is photosynthetic, therefore, light causes algae. Basically, cyanobacteria is the root ancestor of algae, in many different ways depending on what kind of algae you are talking about. Start researching basic biology and plant evolution if you want to fall down this rabbit-hole lol.

As to your question on nitrate and/or ammonia, it’s actually the nitrogen found in ammonia (hydrogen nitride)(NH3), nitrite (NO2), and nitrate (NO3) that all photosynthetic life (some bacteria, algae, and plants) feeds on. Nitrogen, phosphorus, potassium, and carbon are the 3 most important nutrients (macro-nutrients) that must be available for photosynthesis to occur.

To attempt to prevent algae, you can limit light, and nutrients by either keeping the tank dimly lit with little to no nutrients (good luck!), or by having enough plants to use up the nutrients during photosynthesis before the algae does, in a sense out-competing the algae.

It’s a balancing act! I am no biologist, but these are the basics that I can remember from the little biology I took in college. Hope it helps!