Well, someone tell me to crank up the CO2 level in my tank( hopefully without fish) up to 40ppm or more to have plant do more photosynthesis, therefore to have more growth.
I think the whole idea adding excess CO2 to have more growth is just wrong:
We know, CO2 + H2O --light--> glucose + O2
- In biological sense, plant is not a test tube. We can't just throw them some extra CO2 and H2O, and expected them to produce more O2, sugar. It is actually a complex reaction which can only happen in plant cell.
- In a chemical sense, adding one excess reactant will just make another reactant become limited. Therefore, the whole reaction become limited due to lack of 1 reactant.
No offense, just hope everyone will not waste the CO2 to encourage more growth, therefore, to compete with some algae.
You are making a very basic error that many aquarist/plant keepers do:
You make no mention of light.
It, not CO2, is the first link in the chain.
Light drives CO2 demand, so less light = less CO2 demand.
If all you care about is faster growth and more productivity in a certain space, then about 600-700 micrmols of light(this is a lot) and about 30-40ppm of CO2 ought to do it.
So whenever you discuss CO2, uptake, demand, algae etc, light must be addressed.
Clearly through, if you have non limiting levels of CO2 at high light, the same condition will apply at low light.
But you will have a lot more wiggle room with low light.
Now we come to the problem, one that's mostly a USA issue, too much light, the belief that more light is better, can grow plants "better"
Few folks outside the USA have such high light and make this mistake.
They think and assume more is better when it comes to light.
If you want to reduce and control growth rates, thus water changes and dosing and work, reduce the light.
Then targeting a non limiting CO2 concentration is far easier.
I must have been telling hobbyists this for 12 years or more now.
No listens, then whines when they have algae and CO2 issues with their high light.
So they have less leeway with their CO2 and I try and help them.
However, most are poor about testing CO2, and considering the other issues surrounding CO2. CO2 ppm's can change 10X in one hour. How about light? Nutrients?
Nope, not even close.
How much dry weight biomass is CO2?
40-45% or so.
That's a lot more than the 1% or so of N.
Other things play a large role in CO2 beside "adding more".
1. Good flow through if you use a CO2 reactor, you need to have enough current to deliver the CO2 to the plants at the right rates.
2. As plants grow, they dramatically reduce currents inside tanks, so pruning is critical to maintain stability. You can make up for this by adding high current in the tank and/or CO2 mist.
3. Good surface movement, this helps the fish and prevents lower O2 levels, and degasses excess CO2 rather than having a high build up. Yes, you lose some CO2, but it's well worth the trade off here.
4. Good plant growth, if you limit PO4, you will not demand nearly as much CO2. When Paul and Kevin suggested PMDD, they suggested limiting PO4 to 0.1ppm or so(most of which in not bioavail due to being organic forms of P), thus only needed 10-15ppm of CO2 to provide stable non limiting amounts.
So both light and nutrients can cause variances in CO2 demand for the tank.
It's not some simple one parameter model here.
There are other things far too many folks over look and make poor assumptions about. Then they piece meal the advice I give, and only hear one part, "add more CO2".
When I say such things, it assumes they are already doing well wit the nutrients, routine filter maintenance, water changes, pruning, have enough current etc and right amount of light.
They often say "yea, yea, everything is perfect there" when I ask...........
I'm not perfect, so I know they are not..........I have to check and go through carefully to make sure things are correct.
Do not be so sure of your assumptions.
Check and make sure.
Think about the plants, not just the chemistry.
What makes a plant under water grow?
A simple, but good question that is not an easy answer.
This might help you resolve the notions you have hopefully.
As well as help others.