# Stable CO2 - What does it mean exactly?



## Aeropars (17 Apr 2008)

Hi Guys,

My problems are well documented but I'm not sure what people exactly mean when they talk about stable CO2.

Are we talking about having the tank at a target CO2 level at lights on and then maintaining it all day? 
Are we talking about lights and co2 coming on and then the CO2 gradually getting to the desired level and then maintaining it?

The way I'm currently add co2 is having the solenoid turn on 2 hours before lights on. I've came home from work yesterday and it was there or there abouts where I wanted it (judging by my PH monitor which is now used as a failsafe) but throughout the evening it got slightly more concentrated the later into the evening. How do you guys work it?

Lee


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## ceg4048 (17 Apr 2008)

Hi Lee,
         Stable CO2 can be thought of as a concentration level that is sufficient for the available light that is more or less constant throughout the photoperiod. 

Carbon fixation is a complicated procedure which involves many chemical reactions but the most important reaction is the first one. This involves the capture and transport of the CO2 by an enzyme called "ribulose-1,5-bisphosphate carboxylase/oxygenase" shortened to "RuBisCO".

The production of the enzyme RuBisCO is tightly coupled to, and controlled by the concentration of ambient CO2. For "X" amount of CO2 present the plant produces "Y" amount of RuBisCO. This maximizes the efficiency of carbon fixation. If the quantity of available CO2 suddenly drops the plant then has to reconfigure it's chemistry to raise the amount of RuBisCO. Similarly, if the CO2 rises, a RuBisCO production decrease is accomplished. This would be OK if RuBisCO production and reconfiguration in higher plants were quick, but as it turns out, this procedure is very slow - a week or two may be required. Evidently, some plants adapt more easily than others.

You can see therefore that a fluctuating CO2 level causes a rise and fall of RuBisCO production, and during this time the photosynthesis machine struggles to produce the sugars and proteins required for growth while the plant is busy attempting to adjust the machinery to the CO2 levels.

This is only relevant of course during the photoperiod. None of this matters during the dark. If you turn the lights on and the CO2 levels are low, this yo-yo begins. The morning is more important because this is when the plant transitions from 100% respiration to food production. Near the end of the day the plants start to "close up shop" so the levels are not so important then. You can often see this behavior on plants like L. aromatica or D. diandra as they start to fold up their leaves near the end of the photoperiod.

The trick is to have high stable CO2 levels by the time the lights come on but it's OK if the levels slowly trail off in the afternoon. Remember that the plants are removing CO2 from the water so enough CO2 has to be added to compensate. The easy way out is to have 24/7 CO2. This works fine and doesn't require any acrobatics with a solenoid. The disadvantage is that you can't get as high a level of CO2 during the photoperiod without killing the fish and the CO2 consumption is wasted. The fish can also have a problem in the morning when oxygen levels are depleted and CO2 levels are at their highest.

Algae have no trouble adjusting to fluctuating CO2 levels and it may even be that fluctuating levels help to trigger some algae types such as BBA. One of the first indications of lower than expected CO2 is the appearance of green hair algae. I see this when I'm not paying attention and the CO2 cylinder is gets low causing an injection rate falloff.
I either have to adjust the needle valve or swap out the bottle and/or temporarily lower the light. Unfortunately it then takes weeks to stop the hair algae production. I don't panic though because I realize that the RuBisCO production stabilization takes time. I just get the toothbrush out and twirl away once or twice a day. It's when you misread the signs and take inappropriate action that the trouble begins. Some people panic and decide to stop dosing, which is of course completely absurd.

Hope this helps clarify.

Cheers,


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## Aeropars (17 Apr 2008)

Thanks for the comprehensive explanation ceg.

I should ensure that my CO2 level is at its highest concentration by light on? Even if its close, is this too much fluctuation?

Incidentally, how long does it take you to get to the right level? I think i'm close at 2 hours but not quite to the maximum. I tent to look at the ph monitor which i note the start ph and when i 1ph drop has occured i know i'm about there on the 30ppm


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## ceg4048 (17 Apr 2008)

If you are close that will be good enough. What you don't want to be doing is to be fooling around with the needle valve constantly because then you get swings in the concentration level which cause problems. This is what can happen with a pH controller as it dumps gas then shuts it off , then dumps as it tries to maintain pH. Mild variations seem to be tolerated. I have a large tank so the "inertia" is high. I turn my gas on about 1.5 hours before lights on, however, my lights-on is only the first 30% for the first hour or so of total wattage. I reckon that this lowers the CO2 demand which gives me a wiggle room. By the time the remaining 70% of the lights come on I'm pretty close to max saturation levels. Again, it's impossible to be exact, but close enough. You can get a rough idea by seeing the pH change as you've noted. You can record the pH values over the course of the day and build up a profile to see peak values. As long as you're not using the pH values to calculate CO2 then you're OK. The pH profile can be used as a tool to help you to visualize the concentration levels.

Cheers,


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## tanker (18 Apr 2008)

Hi ceg, u mentioned that in the morning, the plant start to turn to food production and then gradually stop towards the end of the day. currently i swithc on my light and CO2 together  at about 11am until 7pm (will on CO2 earlier once i get a second timer). is this timing a little too late? or it doesnt matter as long as i've been consistent on the timing?


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## ceg4048 (18 Apr 2008)

Hi tanker,
               Consistency is always a good thing where plants are concerned, that's for sure. Generally however, I'm of the opinion that it's too late - but every tank has a slightly different set of dynamics, so we have all these rules of thumb. It's possible that if your tank is tightly covered it may retain enough CO2 overnight so that the concentration level at lights-on is not too low. It may also be that your lighting is lower than the average so that at lights-on the demand is not very high. Your injection rate may be better than the average so that the level rises rapidly. Your flow/distribution might be better than average. Any combination of these factors could swing in your favor - or not. The proof of your pudding is whether you see those telltale strings of hair algae popping up here and there, or whether you have leaves falling apart or turning brown, or if you are having trouble getting some plants to survive after you initially place them in your tank. You would be amazed at how many problems are directly related to this issue. Something like Cryptocoryne rot for example. Everyone seems to accept this as inevitable, but I disagree. My crypts never rot, whether I move them around or put them in the tank brand new (or even when I pour boiling hot water on top of them). I'm convinced that this is CO2 related.

So a simple adjustment like turning on the gas an hour or two before lights-on will make a difference, especially if you are on the wrong side of some of those other factors mentioned above.

Cheers,


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## tanker (18 Apr 2008)

Thanks for the explanation ceg. I've therefore made up my mind to get another timer for the CO2. i think i had been dosing too little CO2, in addition to bad ferts without enough NPK... more CO2 for the last 2 days had resulted in plants pearling like mad. But the ones far away from the diffuser are still not so great, probably because of the flow and these are glosso (rather unhealthy) 

the question i wanted to ask was, if i'm to consistently swithc on the lights from 8am to 5pm, CO2 1 hr earlier, does it make any difference if i'm to do it from say 1pm to 10pm? will the plants go haywire as it is supposed to 'sleep' at night? sorry this is lighting in a CO2 tread


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## GreenNeedle (18 Apr 2008)

Ceg I notice you say you think cryptrot may be CO2 related.  This may be true but I think it will differ for diferent people.  They always rot for me as does Blyxia.  I put it down to my water parameters being very different from whenst they they came.  When I move them within the tank I have no such problems.

As for lighting it doesn't matter when your 'day' is lightingwise.  Mine is 2pm-midnight.  As long as its reasonably consistent each day and there is no direct sunlight to 'confuse' things then it should be the same for fish and plants once they get used to it.  Mine seem to as the plecs always get really lively at 11ish (1 hour before dark) and the Rams start to come into the open at 1pm ish (1 hour before lights on)

Andy


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## ceg4048 (18 Apr 2008)

tanker,
           A lot of people change their lighting/CO2 schedules to coincide with when they are at home as opposed to being at work. This is a great idea. If you shift the timing of the tank lighting and CO2, the plants will do fine. They will adjust to the new schedule. I think that's what you are asking right? The plants don't care what time it is, only what rhythm the photoperiod has. Plants don't sleep, they only perform different functions (non-food production related) in the dark.

Cheers,


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## ceg4048 (18 Apr 2008)

Hi Andy,
            Undoubtedly water parameter change has some influence. Yet some people report experiencing rot just moving the crypt within the same tank, so how could that be explained? Possibly flow differences within the tank maybe? My suspicion is based on having tanks in different countries/cities with completely different water parameters, including having used RO. The one constant in my observations is that regardless of what water the crypt came from or was put into, if the CO2 was very high no rot was observed. Similar story with blyxa although I have much less experience with this plant. Again, I now tend to drive my CO2 deep into the yellow so that is a different CO2 regime. It could be that very high CO2 saturations negate the effects of water parameter differences.

Cheers,


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## Garuf (18 Apr 2008)

Stable co2 is for me been something of a holy grail, I get evaporation that negates that it never seems to be stable by looking at the drop checker. When the tank is full the drop checker ran yellow, when the evaporation of 2 days was left un-topped up It barely turns green, what's going on there and are there any ways to combat this?


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## GreenNeedle (19 Apr 2008)

This is probably down to circulation as when the level drops the outlet (whicever type you have) is closer to the surface and therefore the circulation tends to change.

When I get evaporation the Lily is closer to the surface and there isn't as much of a 'push' to carry the bubbles.

Andy


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