BBA is related to stable
Stable CO2 allows the plant to adapt to the Carbon available.
I'm not just saying this.
There's some very good biochemical and enzymatic reasoning behind it.
And it makes a lot of sense
Plants make an enzyme called Rubisco. This represents the largest fraction of nitrogen and protein in the plant and, well....the entire world!
It's an expensive enzyme to make.
Plants up and down regulate the production and also degrade it for use in other situations when in excess. Plants are lazy. If they have too much Rubisco not doing anything useful, they will allocate and partition the Nitrogen from the enzyme and degrade it.
So aquatic plants certainly do adapt to high, medium and low CO2 content, there's plenty of recent direct evidence for this in aquatics and most every terrestrial plant as well.
It's not a special case adaptation to their environment in other words.
It's very broad, "generalizable" and a common sense regulation.
No plant should be without it.
In a non CO2 enriched tank, plants adapt to low CO2, takes maybe 1-6 weeks depending on the species, by making a lot of Rubisco and scavange for any CO2. As long as the CO2 is nice and low, the plant maintains this cocentration/enzymatic activity of Rubisco.
Contrast this with a high CO2 tank where the plants get a stable level of say 30ppm.
These plants become fat and lazy. They do not produce much CO2 fixing enzyme because, they do not have to after a few weeks of adaptation. We see plants slowly acclimating to such tanks just like the non CO2 ones.
Once they settle in, they really take off.
They can devote far more resources to growth than CO2 uptake.
Now ask yourself this question: what would happen if I added CO2 to a non CO2 tank? Would this hurt/harm growth? No, but the CO2 would be removed very fast and then the Nitrogen PO4, K, Traces etc.
This is fine if you add the other downstream nutrients like N, P, K, Fe etc.
But if not?
Folks think enriching w/CO2 = algae.
Now the next question you most likely should ask about this: what happens if you take a high CO2 adapted aquatic plants, and place it in a tank with 50% less or 75% less or 90% less CO2 and also add high light (this will remove the CO2 much faster than the lower light non CO2 approach!!) ??
The plants now have very little Rubisco since they are adapted to high CO2 and are "lazy". You also add lots of light which makes the uptake demand (but not supply) faster.
Your plants cannot respond quickly to this low concentration. It takes time
for the plant to make more enzyme. It takes them a few days, weeks to make more. So if the CO2 drops say from 30 ppm to 15ppm during the day, the net effect is that the plants are CO2 "starved", limited for a peroid of time. This is not a black and white effect, there is a gradation of carbon limitation over a wide range. After a few weeks of stable conditions, the plants are fine again, but now the adult algae are there and tough to get rid of. So you pick and clean things up and prune and pick on the adult algae and keep things in good shape for the plants.
Suppose you are NO3 limited? Then the ability to make the enzymes required when conditions change like this becomes even more troublesome.
Alagae have very low CO2 demand, but they also have far less trouble responding to CO2 changes in their environment. They prefer high CO2 as well, but have much less trouble with variations and making Rubsico or HCO3 uptake and can respond very rapidly to such changes, whereas the plants, which are much larger, take more time.
That time difference in CO2 adaptation allows some species of algae to get a foot hold and germinate. Think about in terms of nature. It's a good adaptation if you are an alga to respond quickly to CO2 variation.
If you have low light, there's much less issue with all this and shows why it helps to reduce lighting rather than limiting NO3, PO4 etc.
Light first drives CO2 uptake!! Less light= less CO2 demand.
Now why do take grow wekk for awhile, then get algae a bit later? As plant biomass increases, so does CO2 uptake, assuming the CO2 is going to be the same the entire time is a bad idea. If you have 3x the plant biomass , you are going to have a lot more CO2 demand.
Therefore: good consistent pruning, adding a bit more CO2 as tanks grow in well and biomass increases, watching the CO2 conternt over the lighting cycle(rather than one discrete point during the day) and giving things time once you do stabilize the parameters will help a great deal.
Aquarist have a lot of issues with CO2, they whine, they cry, they bellyache, they speculate, they blame the innocent players such as NO3 or PO4 or the advice. But few really look at CO2 critically in terms of of why it helps, why it works, or also, why it does not work
sometimes. My CO2 is high and I'm certain it's perfect, why do I still have algae with EI or with ADA?
Then the counter, why doesn't Amano or Tom Barr, or other folks have algae then?
We add a fair amount of nutrients, I use the same type of substrate as Amano and a lot of other substrate, and probably more light than Amano, most of you use more light than Amano BTW.
Well what is the solution then? Keeping a closer eye on CO2, making sure things are stable, kept up on, pruned well, being a lot more humble and doubtful of your abilities and assumptions about what is causing issues for you. If you have an issue, try and figure it out, not by the advice so much, rather test and give the test time.
Work from this downstream appraoch if something does come up: light(easy to change generally)=> CO2 (often hard to measure, takes many readings and a careful eye)=> NO3=> K=> PO4=> Mg=> Ca => traces.
EI takes care of the nutrients, light and CO2 are all that are really left.
Obviously, from and management prespective, less light(duration to some degree within a fairly wide range and more importantly, intensity) will help reduce the deamnd for all down stream nutrients since it drives CO2 uptake and carbon regulates N, which regulates other processes such as enzyme production of Rubisco.
Patience is another issue, how long should we really try and keep up on things?
No simple answer there, but if you can do a fair amount of work to do that for a few weeks, typically 3 or so, then you should see some improvement.
If not, change the approach.
It does not mean or imply the tank will be spotless, but it should be on that way, no new algae growing/formed etc.