[ZChalk]

The addition of pressurized Co2 is causing the algae bloom plus the nutrients in the water (nitrate issues). Without pressurized Co2 being added to the water, there was only a low amount of Co2 (limiting factor). There was enough Co2 to foster plant growth and trace amounts of algae growth - primarily because you actively culling the population size. Adding pressurized Co2 is comparable to dumping gasoline on to a smoldering fire. With abundant amounts of Co2 in the water, the algae is converting it into growth, hence the bloom you are seeing.

Algae is one of the fastest growing and most efficient simple plant-like organisms. Plants cannot outcompete algae in Co2 uptake, however plants can contribute to the overall uptake of Co2. The biochemical reaction is the same (photosynthesis) but the faster a plant grows, the more Co2 it will use per second. Algae given the right conditions (light + water + co2 + nutrients) can double its size in 2.2 hours (i.e. picochlorum renovo). Why the fast growth? They are simple organisms that lack the organization of higher plants with leaves and vascular tissue. Algae per size is so efficient at growing that they are used in algal cultivation (see photobioreactors) as a source of renewable biofuels.

 

[ZChalk]

Its okay to disagree but aquatic Plant and Plant like Organism Growth = Light + Co2 + Nutrients.

Stirring the substrate (released decomposing organic matter) with the addition of the new plants caused the spike in nitrate. The hair algae likely tagged along with the introduction of the new plants or water (new fish) from the LFS. I don't know the tank; I don't know what types of algae was present before.

Regardless if you double the dose of Co2 and fertilizer, all plants and plant like organisms will benefit. Algae just grows a lot faster - that's not conjecture, it's a fact. When algae blankets a glass wall think microscopically how many new algae organisms have been created.

If plants are removed, it will be compensated with more algae growth given everything else is constant. So the options are to attack the algae by physically removing it, chemically treating it, or introducing something to eat it...and/or to reducing the overall tank's plant growth by changing the lighting period, Co2, or nutrients. Note, all plants are affected in some manner, algae more observable since it grows faster and because the poster would be actively looking for the change.