# CO2 stability during photoperiod?



## gray_ (27 May 2019)

It's frequently mentioned that CO2 must be stable during the photoperiod, but what exactly does "stable" mean? How stable?

During my photoperiod (also including the ramp up and ramp down times of the lights) my pH varies within a range of 0.1. Is that stable enough or do I need more stability?

I spent the bank holiday watching the clock and testing the tank, much to the other half's annoyance. My degassed tank pH is 8.21, here's the pH profile:


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## Edvet (28 May 2019)

It takes 7 hours to get to a stable situation, this i would try to improve. Try to get max pH drop in 1-2 hours.
It could be this situation works but it's dependent on lighting levels (lower light decreases CO2 demand).


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## Craig Matthews (28 May 2019)

I'm having the same issue, my pH is at around 7.5/7.4 at lights on and at the end it's about 7.2/7.1 just wondering how you keep it at a certain level. I'm guessing it's the equilibrium of surface movement  Vs injection so it's finding correct level of these + lighting levels.


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## Zeus. (28 May 2019)

I 'cheat' when it comes to controlling pH/[CO2] in my 500l tank, I use a variable CO2 injection rate via my PLC (*How to use a PLC to control your fish tank.) *so my 1.0pH++ drop takes place in 30 mins then remains stable for rest of CO2 period. Its not cheating its another way of controlling the [CO2]


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## Craig Matthews (29 May 2019)

Lovely looking bit of kit that Zeus, if only I was upto scratch


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## tiger15 (29 May 2019)

gray_ said:


> It's frequently mentioned that CO2 must be stable during the photoperiod, but what exactly does "stable" mean? How stable?
> 
> During my photoperiod (also including the ramp up and ramp down times of the lights) my pH varies within a range of 0.1. Is that stable enough or do I need more stability?
> 
> ...


What is the point of getting stable CO2 during the photo period?  Even in nature, as measured in many ponds, CO2  fluctuates throughout the day and night due to respiration addition and photosynthesis depletion.  It takes time for CO2 to dissolve in water and photosynthesis to deplete it in reaching a balance of gradual change.  Any artificial system that can instantly turn on and off CO2 at stable concentration can be detrimental if the system malfunctions.


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## Zeus. (29 May 2019)

tiger15 said:


> What is the point of getting stable CO2 during the photo period?





ceg4048 said:


> we know that when the plant senses that high concentrations of CO2 is available, it responds by reducing the production of expensive Rubisco. When it senses a lower CO2 concentration it must increase Rubisco production, however because this protein is so complicated and heavy, the increased production requires 2-3 weeks in order to change the density in the leaf to match the new gas concentration level. So it is much easier to reduce production than it is to increase production. When increasing gas injection therefore, it hardly takes any time to see an improvement in health. When lowering the concentration, the plant will suffer because it must now ramp up Rubisco production to account for the loss of CO2 availability.
> 
> When increasing the light, the plant must reallocate resources from Rubisco production/maintenance in order to deal with the increased radiation. This may entail new pigment production for protection. When the light is reduced, the plant then reallocates the light gathering proteins and can devote them to Rubisco production/maintenance.



 so stable is better


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## Craig Matthews (29 May 2019)

I'm wondering if these ponds get bba if they fluctuate so much?


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## Zeus. (29 May 2019)

Well my pond gets a seasonal algea bloom, can get loads of blanket weed at times. Never looked for BBA but Im sure its there all the same, I just accept it.


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## tiger15 (29 May 2019)

I referred to natural ponds, not man made ponds, which differ day and night.  My outdoor tubs get green water and filamentous algae, but never bba.  I put out  plants infected with bba in the tub and within weeks, all bba are gone.


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## Craig Matthews (29 May 2019)

So yeah a natural/man made pond would have a slow incline/decline in co2 concentration as it's only natural equiblibrium co2 entering the water rather than a injected tank where a slight blip in equipment would have a big impact where co2 concentration is much higher and forced out of water at a high rate through equiblibrium and cause a much more severe fluctuation more rapidly


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## rebel (30 May 2019)

I don't see a need to change your profile unless you are having issues.


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## Geoffrey Rea (30 May 2019)

Hi @gray_ 



gray_ said:


> It's frequently mentioned that CO2 must be stable during the photoperiod, but what exactly does "stable" mean? How stable?




Perhaps a better mindset is to consider Co2 in relation to all the other components in the system, using the best of our observational abilities across time to achieve this. Empirical evidence is all we’ve got most of the time unless you want to fork out on well calibrated equipment. In a high tech system it’s desirable that all of these in principle, light/Co2/o2/Macro nutrition/Micro nutrition etc, are adequate (or above but not to a toxic/unnecessary level) but never below. This is true of Co2 and all other (inorganic) nutrients that we put into the system regularly in high tech setups.


The moment the light comes on most of us want that Co2 to be at 30ppm (an arbitrary figure to some extent) saturation in the water in high tech systems. This gives plants adequate carbon to grow if all other components are also adequate or above the plants needs.


But plants begin their uptake of Co2 at lights on (or a little after) and the amount of Co2 saturation in the water will potentially drop/dip as they uptake Co2. Can’t prove this but would say this dip will decrease the overall efficiency of the plants in your tank for the rest of the period as experience has shown they don’t get on as well if Co2 saturation isn’t maintained above their needs throughout the photo period. The dip makes this saturation level a moving target and is an example of what we specifically mean by instability of Co2 levels in a photo period.


Zeus references Ceg4080’s statement: 

“When it (plant) senses a lower CO2 concentration it must increase Rubisco production, however because this protein is so complicated and heavy, the increased production requires 2-3 weeks in order to change the density in the leaf to match the new gas concentration level. So it is much easier to reduce production than it is to increase production.”


This is undesirable.


In a high tech tank you’re driving the plants hard with high light, this needs to be married with high Co2 to match this fast growth. This takes some experience. A drop checker tells you what’s going on two hours ago, not right now. If your fish are gasping but the drop checker isn’t green yet, which are you going to trust?


One way around this scenario is to diffuse Co2 at a higher rate but to have good surface agitation. This should gas some Co2 off (a downside) but caps the level of Co2 to an extent whilst providing good gaseous exchange and specifically adequate levels of oxygen for bacteria/fish/snails/shrimp at the beginning of the photo period. Photosynthesis will make o2 readily available later in the period. Tuning Co2 in efficiently like this using just a dual stage reg and a timer is gained through good observation and experience. Watch your fish, watch your plants. They’ll give you all the info you require to keep Co2 ‘stable’.


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## tiger15 (31 May 2019)

Dennis Wong has a scientific explanation on how to achieve stable CO2 by ramping up both gas exchange and CO2 injection rates.

https://www.advancedplantedtank.com/gas_exchange.html

Looking at the OP profile, he has already achieved substantial stability and I don't know how much more refinement can be made.

I think it's an over kill to attempt absolute stability.  As long as elevated CO2 is attained within narrow range consistently during each photo period, plants will cope with appropriate enzyme production.  Overly aggressive to achieve absolute stability at light on time can risk hitting lethal level by accident as very high CO2 injection rate plus long pre injection time are needed.


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## Zeus. (31 May 2019)

tiger15 said:


> Looking at the OP profile, he has already achieved substantial stability



Agree



tiger15 said:


> I don't know how much more refinement can be made.



Can but would cost time and money



tiger15 said:


> Overly aggressive to achieve absolute stability at light on time can risk hitting lethal level by accident as very high CO2 injection rate



Yes it can be tricky with high BPS - heres vid of mine





tiger15 said:


> high CO2 injection rate plus long pre injection time are needed.



Yes high BPS but I manage it in 30 mins but do have a variable twin injection rate, over kill 'Yes' but stable


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## Geoffrey Rea (31 May 2019)

tiger15 said:


> Looking at the OP profile, he has already achieved substantial stability and I don't know how much more refinement can be made.



Increasing plant mass, more requirement for Co2. Dynamic system. Not negating your point as I agree, just adding this point to highlight that requirements can change. Any future deficiency solved by increasing Co2 as plant mass increases if you’re running it close/efficiently or dropping the tank temperature to improve Co2 saturation into the water column (plant and animal species taken into consideration before lowering temps). Temperature drop also slows metabolism so again, dynamic and in system with other variables.

Alternative is capping the upper saturation rate through gassing off with surface agitation which was initially proposed. Just putting it forward as a ‘set and forget’ style to Co2. Many roads to Rome.

I listen to the plants and fish, they don’t need calibrating and are brutally honest about your Co2 regime.


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## Zeus. (31 May 2019)

Geoffrey Rea said:


> highlight that requirements can change.



Yes

IMO Dennis Wong Method of having higher injection rates with increase surface agitation compensates for the plants changing CO2 requirements better than a lower injection rate with less surface agitation, so once set they will be less need for adjustments of BPS as long as the surface agitation remains fairly constant


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## alto (31 May 2019)

Zeus. said:


> so stable is better


I followed up your last repost of this (awhile back  it’s likely been posted since as well) - I’m just a bit of a biochemical sceptic 

Anyway depending on plant type, there are several CO2 sequestering/storage methods - which are often demonstrated in papers via rices (fast growing, readily available, AND funded research  ... but these are not de novo biochemical pathways, rather they are shared by multiple plant types) ie plants are very adaptable 
Some plants don’t just _appear_ to grow in the dark, they actually uptake CO2 and elongate (grow) - of course this biochemical pathway comes at a certain cost (reduced production of other CO2 sequestering molecules etc) and may be a time limited adaptation (again depending) 

My Endgame : “stable” CO2 is not really that important IF it falls withIn a threshold range, available CO2 is (perhaps more?) important

Of course this is an easy belief for me, as my aquariums have always run with erratic CO2, erratic lighting schedules, erratic water change routines, 2-4x water volume turnover rates, limited water column nutrients (nutrient rich substrate ... which will always be “leaking” to some degree) etc, etc ... I’m just a Lazy Aquarist yet my tanks always have minimal algae (I do pay _some_ attention  ) 



Zeus. said:


> so my 1.0pH++ drop takes place in 30 min


I suspect this is challenging for livestock


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## tiger15 (1 Jun 2019)

Zeus. said:


> Yes high BPS but I manage it in 30 mins but do have a variable twin injection rate, over kill 'Yes' but stable


Yes, it can be done with proper instrumentation.  But what if the instrument malfunctions, say the timer gets stuck, then it can reach lethal level quickly.  

I am concerned for the live stock.  So I prefer gradual stability to quick stability to avoid the possibility of hitting lethal level accidentally.  Plants are adatptable to variable CO2 in nature, so I am not convinced that the marginal benefit of quick stability is worth the risk.


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## Zeus. (1 Jun 2019)

alto said:


> I’m just a bit of a biochemical sceptic



Which is good as you always questioning peoples theories 



alto said:


> My Endgame : “stable” CO2 is not really that important IF it falls withIn a threshold range, available CO2 is (perhaps more?) important
> 
> Of course this is an easy belief for me, as my aquariums have always run with erratic CO2, erratic lighting schedules, erratic water change routines, 2-4x water volume turnover rates, limited water column nutrients (nutrient rich substrate ... which will always be “leaking” to some degree) etc, etc ... I’m just a Lazy Aquarist yet my tanks always have minimal algae



But if your getting the results your happy with good plant growth minimal algae jobs done stable [CO2] is irrelevant 



alto said:


> I suspect this is challenging for livestock



No, fish shrimps quite happy. when I was doing a bigger pH drop yes a few would be gasping just before lights on, but since I increased my target pH no issues. My take on it is if the pH drop takes 2-3hours and the livestock are fine with it, why should the same pH swing bother them is it takes 30 mins !

I have never knowingly lost livestock though CO2 in my 500l tank, cant say the same for my 50L shrimp/pot tank  which has single CO2 injection and a 2+ hour pH drop time



tiger15 said:


> Yes, it can be done with proper instrumentation. But what if the instrument malfunctions, say the timer gets stuck, then it can reach lethal level quickly.



PLCs dont stick 'How to use a PLC to control your fish tank' @ian_m gives the reasons why PLCs are so good in the first post.

Then I have a pH controllor that signals my PLC which then switches off one the the twin CO2 lines when target pH is reached for the rest of the CO2 period, PLC also has a little software that varies the second CO2 injection rate whilst the lights ramp up. Over kill yes but does allow me to control the [CO2] with more finesse  

Like Ian I enjoyed doing the PLC and programming it.


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## tiger15 (1 Jun 2019)

Zeus. said:


> I have never knowingly lost livestock though CO2 in my 500l tank, cant say the same for my 50L shrimp/pot tank  which has single CO2 injection and a 2+ hour pH drop time
> 
> PLCs dont stick 'How to use a PLC to control your fish tank' @ian_m gives the reasons why PLCs are so good in the first post.
> 
> ...


You are blessed not having accidents with your sophisticated set up.  I had experienced a disastrous wipe out of livestock once during my vacation.  My set up was unsophisticated, just two timers to separately control lighting and CO2 so I can stagger  CO2 and photo periods.  One timer got stuck and dumped  all CO2 in my 2 weeks absence, and I returned home with smelly fish soup.  So I am scared of instrument malfunctioning and prepare for it to happen. Since the disaster, I reduced CO2 injection rate and reset one timer to control both so CO2 and photo periods periods will always be synchronized.  I haven’t observed any difference in plant heath since the switch even though CO2 is less stable  now.  This is why I questioned the benefit of absolute CO2 stability.


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## Zeus. (1 Jun 2019)

tiger15 said:


> You are blessed not having accidents with your sophisticated set up.



Dont think I've been blessed with anything, I made a choice/investment in an industrial reliable timer as I am well aware of the limitations of cheap timers and they can/do fail sooner or later, so IMO luck had nothing to do with it . The PLCs are not cheap but neither was my setup so it was IMO a great investment as one stuck timer when away all that time and effort can be lost . Plus so easy to adjust the timers/software once your use to it, light intensity/duration ferts etc etc etc I've had my PLC setups for about two years Ian has had his much longer and they have never missed a beat


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