Myth? Crank up CO2 will help plant do more photosynthesis. - The Planted Tank Forum
 
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post #1 of 12 (permalink) Old 02-10-2008, 10:29 AM Thread Starter
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Myth? Crank up CO2 will help plant do more photosynthesis.

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.


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post #2 of 12 (permalink) Old 02-10-2008, 11:16 AM
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In general, people do not have excess CO2. It is difficult to achieve excess CO2. While it is true that plants need light, CO2, nitrogen, phosphate, potassium, and trace elements, CO2 is the most commonly lacking item on this list. It is probably the hardest to keep stable, and the most expensive, next to light.

30 ppm is the general target value for CO2. 40ppm may work depending on your setup. It could be dangerous to do this with fish in the tank. Usually, a lack of oxygen, not an overdose of CO2 is the cause of death in fish with pressurized CO2.

While putting them into practice can be quite difficult, the basic principles are not that complicated. Here are some good websites to begin with:
http://www.rexgrigg.com
http://www.barrreport.com/you-new-aq...ts-start-here/

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post #3 of 12 (permalink) Old 02-10-2008, 01:46 PM
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When I cranked up my co2, the only thing that grew faster was cyano. I turned it back down and the cyano went away. Everything in balance is what makes plants grow faster. I myself am still learning what that balance is.
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post #4 of 12 (permalink) Old 02-10-2008, 08:03 PM
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Quote:
Originally Posted by stagius View Post
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:

Light.

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.

Moral:
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.

Regards,
Tom Barr




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post #5 of 12 (permalink) Old 02-10-2008, 08:08 PM
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Quote:
Originally Posted by fishscale View Post
In general, people do not have excess CO2. It is difficult to achieve excess CO2. While it is true that plants need light, CO2, nitrogen, phosphate, potassium, and trace elements, CO2 is the most commonly lacking item on this list. It is probably the hardest to keep stable, and the most expensive, next to light.

30 ppm is the general target value for CO2. 40ppm may work depending on your setup. It could be dangerous to do this with fish in the tank. Usually, a lack of oxygen, not an overdose of CO2 is the cause of death in fish with pressurized CO2.

While putting them into practice can be quite difficult, the basic principles are not that complicated. Here are some good websites to begin with:
http://www.rexgrigg.com
http://www.barrreport.com/you-new-aq...ts-start-here/
Well, 30ppm is a non limiting level at most any light level for common aquatic weeds, it may be higher/lower for other species(no one has studied most of the weeds we keep with gas exchange and growth rates and O2 production levels) . If you have 1.5 W/gal of light, strong PO4 limitation you might only need 10-15ppm of CO2 to be non limiting.

If you have 1 W/gal, no CO2 additions might be needed.

And so on........

The above previous past I made also addresses some of the issues surrounding CO2.

Now even the most experienced and well seasoned aquarists, myself, and Amano , you name them, have done and still do from time to time.

So if we have issues from time to time, I know other folks do. A few get lucky, but some do not and fewer yet stay lucky, most everyone eventually has an issue.

Regards,
Tom Barr




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post #6 of 12 (permalink) Old 02-10-2008, 08:34 PM
 
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What about "high light" plants? Can they be grown at 1.5 watts or do you just have to make this sacrifice? I've thought about cutting my lights in half - using just 2 65 watt bulbs instead of 4 on my 75 gallon. That would be about 1.7 watts per gallon, but of course the watts per gallon rule isn't straightforward either.
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post #7 of 12 (permalink) Old 02-10-2008, 09:28 PM
 
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Question

Quote:
Originally Posted by loachlady5 View Post
What about "high light" plants? Can they be grown at 1.5 watts or do you just have to make this sacrifice? I've thought about cutting my lights in half - using just 2 65 watt bulbs instead of 4 on my 75 gallon. That would be about 1.7 watts per gallon, but of course the watts per gallon rule isn't straightforward either.
Why not just leave your lighting the way it is and either try "noon-burst" photoperiod or "splitphotoperiod" I have tested both: Noon-burst gives better plant growth but split gives less algae but not a good plant growth - it is a trade off.

Noon-burst: 8 hour photoperiod. Set 2 65 watt bulbs on seperate timer if you can, let them run 4 hours with the other 2 65 watt bulbs on a seperate timer as well. After 4 hours of the 2 65 watt bulbs, set the timer to come on so both sets of 2 65 watts run a total of 4 hours and one set only runs 4 hours. Total photoperiod is still 8 hours.

or

Split Photoperiod: Run your current lights full throttle with a siesta in between. set them on a timer, so they remain on for 4 hours, off for 2 hours and on again for 4 hours, or if you want a longer photoperiod: 6 hours on 2 hours off and 6 hours on again.

In my 15 gallon Aquasoil II based experimental tanks(no fish but snails are doing great), I have c02 cranked up to 40 ppm, using Estimative Index at 1/2 as per Tom Barr's recommendation, and am running lighting at 40 watts total split photoperiod. On from 10:30 a.m. to 3:30 p.m. , off from 3:30 p.m. to 5:30 p.m. and on again from 5:30 p.m. to 9:00 p.m. Plant growth is crazy, no algae issues whatsoever, and I get to enjoy my tank more after work with the lighting on from 5:30 p.m to 9:00 p.m.
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post #8 of 12 (permalink) Old 02-10-2008, 10:59 PM
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Quote:
Originally Posted by loachlady5 View Post
What about "high light" plants? Can they be grown at 1.5 watts or do you just have to make this sacrifice? I've thought about cutting my lights in half - using just 2 65 watt bulbs instead of 4 on my 75 gallon. That would be about 1.7 watts per gallon, but of course the watts per gallon rule isn't straightforward either.
What HS said +

The spread of light is poor then, you have one thin line of high light coming.

You'd do best with say 3x 54 W T 5 bulbs spaced about 5" apart.

That would give you the most angles and plenty of light for most every species.

I really do not know what a high light plant is in aquatics, they are all for the most part, low light.

And they all can be grown well in higher light also.

That is the trade off with stripe lights using Powercompact bulbs, great for narrow tanks, poor for wider ones.

You have more options in terms to adjusting light using pendants and /or multiple sets of light, or variable control %, like they have in Europe.

Then you can adjust things to suit.
ADA addresses this with pendants and also uses 2 types of bulbs and they are spread far apart(maybe 10") and a HQI in the middle, but only run it for a 2-4 hours a day, this way they do not suck all the nutrients out and then only for a few hours each day, which also places less demands on the CO2.

Still,
Plants are not a test tube with only a couple of variables.
However, let us not go too far the other way, and say that there are too many interactions and variables to really answer the question/s.
Then say warm furry stuff about how we are amazed by nature, how we are just starting to learn about how the aquatic plants grow in the environment.

We know why plants grow better than in other conditions.
Same as most any plant.
That part is no different.
Light, CO2, and nutrients.
What about algae?

Who test that?
Who tries and grows that to learn?
Not hardly anyone(myself excluded).

I'm not sure why some folks try to appeal to all the unknown rather than asking a specific question to answer the unknown.
One method tries to answer a specific question and learns, the other does nothing.

You need not be a scientist, I managed to answer many things without any college. So do many hobbyist.

Regards,
Tom Barr




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post #9 of 12 (permalink) Old 02-11-2008, 04:10 AM Thread Starter
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so basically, assuming light is constant as it is in nature, crank up CO2 will help plant do more photosynthesis. Myth busted or what ?


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post #10 of 12 (permalink) Old 02-11-2008, 04:16 AM
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Myth busted.

and light in nature is not constant.. You got the seasons and cloudy days.
The aquarium setting in general has the most constant parameters for good or bad.


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post #11 of 12 (permalink) Old 02-11-2008, 06:36 AM
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Was that the myth in question?

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post #12 of 12 (permalink) Old 02-11-2008, 06:56 AM
 
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Yeah, I was unaware of this particular myth. Who is saying just to crank it up? I know there must be a few out there, but personally I dont know anyone who has no fish / shrimp in their planted tanks so of course CO2 cant be 'cranked' way high without gassing to death our fish. However if your CO2 levels are very low, and you are using high light, 'cranking' it up to 30ppm should indeed help
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