Well, algae are not limited in their rates of growth , except with light.
Plants?
Nutrients and CO2.
The algae have extremely small CO2 requirements, roughly, 100-10000 x less.
Adding CO2 can help algae grow faster also.
While not adding it does slow algae, typically folks without CO2..........also do not have high powered lights as well.
NH4 and CO2 uptake in plants is highly linked/coupled.
So if you suddenly stop adding CO2, or it goes all over, the NH4 uptake will also.
Measuring small transient amounts of NH4 is tough.
Also, higher light will increase the odds of getting an algae response with NH4 dosing.
So you have several things occuring at the same time, but most of it is CO2/NH4 related.
"Why algae do not grow" should not be your question though.
Rather: how can grow nice plants that are healthy and happy, that's the hobby we enjoy, not algae limitation and killing it etc.
We still need to deal with it etc, but the goal is really focusing on good non limiting nutrients, CO2 etc for the plants.
That is where folks need to place their energy, not trying to outwit algae.
Unfortunately, folks spend way too much time fretting over nutrients, and not enough about having less light and good CO2.
Less light= less demand.
That means you have less trouble and variation in the CO2 ppm content in your tank.
And when something goes wrong, it is not nearly as bad as high light.
Still, folks think if they get CO2, they must get high light, then they have all sorts of headaches and wonder why
So CO2+ lower light, say 1.5-2w/gal of T5's, a decent substrate, like ADA's AS, good current in the tank, lots of algae eaters, good frequent water changes etc, that is easy to deal with and produces nice results.
More light is not better, it's just more work and trouble.
This is a 1.5 w/gal ADA tank as an example:
Regards,
Tom Barr