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[APD] How you can still get BBA with high CO2

This is a post I made some times ago, but a refresher is often
needed as many folks forget, think they are on to something
because they still have BBA even with supposely high CO2 ppm

I've stated that high CO2 stops new growth of BBA. Generally
this appears true. But in some systems, the starting CO2 ppm is
low and it takes time for the CO2 injection method to respond
and get the levels high enough, some tanks go along at a high
levels of CO2, then it slacks off, or the bubble rate slows
down(the most common variance, rather than increasing).Other
systems seem to have high CO2, but it's all over the place and
not particularly stable. Good precise measurement is critical to
testing such notions. But stable over what time frame? Generally
stable for a few weeks is what time frame that applies here, not
for a few days or one discrete measurement.

BBA is related to stable CO2.

Stable CO2 allows the plant to adapt to the Carbon available.
I'm not just saying this, There are some very good biochemical
and enzymatic reasoning behind it....and it makes a lot of

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 its production and also degrade it
for use in other situations when in excess(say under low N
levels but ample CO2). Plants are lazy(or "efficient" depending
on your view). If they have too much Rubisco not doing anything
useful, they will degrade Rubsico, allocate and partition the
Nitrogen to other enzymes and/or tissues.

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 type
of plant regulation. No plant should be without it. Rubisco is
the largest fraction of protein in most any plant. Plants make
sugars from the reduction of CO2 and that's their "food". 

In a non CO2 enriched tank, plants adapt to low CO2 (this takes
maybe 1-6 weeks depending on the species) by making a lot of
Rubisco and this extra Rubisco scavanges for low levels of CO2.
As long as the CO2 is nice and low, the plant maintains this
high concentration/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 (or "efficient" if like a more
positive term). 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 adapted 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 to account for this increased demand. But if not?
Folks think enriching w/CO2 = algae. They often see a peroid of
rapid growth, think everything is fine, then slowly algae
appears. Many non CO2 folks ike the idea they do not need to add
ferts, the fish waste alone supplies the plant's needs. They add
just the CO2, they generally run out of nutrients after a few
weeks and plant demand cannot be supplied/balanced with the
removal of CO2 limitation from the fish waste alone.

We sometimes see heavy pearling after doing a large water change
to a semi CO2 limited tank, you will see a lot of pearling, this
generally, but not always is a good sign that there's room for
improvement with respect to the CO2.

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
increases the uptake demand (but not supply).

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.

Algae 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 and have more developmental issues(such
as smaller tips and twisted leaves, holes in some Hygrophila,
blackened color in Java fern).

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 plants grow well 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 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

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 approach 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 demand 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 in CO2 enriched tanks.
If not, change the approach. Measure the CO2 over the cours eof
the day to see what it's doing through a light cycle, not just
at one single point.

It does not mean or imply the tank will be spotless, but it
should be on that way, no new algae growing/formed etc.

Tom Barr


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