cherubfish pair
New member
I would like to inject it into my fuge for the macro through my auto top-off system.
How can I enrich my top-off water with CO2?
- Thread starter cherubfish pair
- Start date
You really do not want to do this for seawater and there is no need. Many macro's do not feed off of CO2 but bicarbonates. CO2 injection only becomes an issue in any water only if there is a lack of CO2. This is only seen when the pH rises do to all the plant life, that raises the tanks pH, due to CO2 removal. If your plants are not raisng the pH to were it is hard for you to control, then CO2 injection is not needed. This is very rare is seawater except in some heavy planted macro algae aqauriums and not a fuge.
If you are worried about CO2 then just raise the ALk, as for when the Alk raises so does CO2, no matter what the pH. If your tank was 8.3 pH and the Alk 3.5 meq / l you have more CO2 than normal seawater. If you kept that alk and lowered the pH to 8.1 there would be even more CO2 and more than the plants would know what to do with in a fuge or even a tank. Like on the order fo 4 times more CO2 than normal seawater.
If you are worried about CO2 then just raise the ALk, as for when the Alk raises so does CO2, no matter what the pH. If your tank was 8.3 pH and the Alk 3.5 meq / l you have more CO2 than normal seawater. If you kept that alk and lowered the pH to 8.1 there would be even more CO2 and more than the plants would know what to do with in a fuge or even a tank. Like on the order fo 4 times more CO2 than normal seawater.
I agree there is no need. The issue is different than in fresh water where there is much less HCO3-.
Samala
New member
Isnt the question though.. for us.. do macroalgae prefer dissolved carbon dioxide.. or do they prefer carbonate?
I've been puzzling on how to answer this question. A large macro/grass tank, like mine, really sucks down the alkalinity readings over the course of even one or two days. Enough to warrant supplementing the alkalinity much like full blown reefs.
Right now, on one of my test tanks, I am adding CO2 via DIY setup and also supplementing alkalinity to the 3 meq/L level. Now.. I'm adding CO2 only because I couldnt keep the pH below 8.6 (meter tested). I'd attribute that to all the photosynthesis going on in the tank. This tank is also so heavily oxygenated at peak photoperiod times that the plants 'pearl', or release air/O2 molecules at the leaf/frond surfaces.
Increasing flow diminishes pearling activity, probably by helping to disrupt the gas balances and move it all back to natural equilibrium. It also drives pH up as the CO2 is far less effective as the flow increases.
Now.. its really been impossible for me to visualize in my head what is going on for the pH. CO2 levels must be depleted to yeild such an elevated pH.. but CO3 levels are depleted as well. So, do the plants like both, and easily switch between them? Or, are they only using the CO3, and my CO2 additions are just a nice pH managament approach?
And then there's the seagrass to consider. Which, we know from actual published papers, will use CO2 in suspension. Impacts of CO2 enrichment on productivity and light requirements of Zostera marina. But they'll also use carbonate instead. Again.. do they prefer one over the other? Is growth better using one over the other?
And.... at the end of the day.. is there an application of this knowledge we've come up with (preference, uptake rates perhaps, etc) to marine planted or refugia tanks?
>Sarah
I've been puzzling on how to answer this question. A large macro/grass tank, like mine, really sucks down the alkalinity readings over the course of even one or two days. Enough to warrant supplementing the alkalinity much like full blown reefs.
Right now, on one of my test tanks, I am adding CO2 via DIY setup and also supplementing alkalinity to the 3 meq/L level. Now.. I'm adding CO2 only because I couldnt keep the pH below 8.6 (meter tested). I'd attribute that to all the photosynthesis going on in the tank. This tank is also so heavily oxygenated at peak photoperiod times that the plants 'pearl', or release air/O2 molecules at the leaf/frond surfaces.
Increasing flow diminishes pearling activity, probably by helping to disrupt the gas balances and move it all back to natural equilibrium. It also drives pH up as the CO2 is far less effective as the flow increases.
Now.. its really been impossible for me to visualize in my head what is going on for the pH. CO2 levels must be depleted to yeild such an elevated pH.. but CO3 levels are depleted as well. So, do the plants like both, and easily switch between them? Or, are they only using the CO3, and my CO2 additions are just a nice pH managament approach?
And then there's the seagrass to consider. Which, we know from actual published papers, will use CO2 in suspension. Impacts of CO2 enrichment on productivity and light requirements of Zostera marina. But they'll also use carbonate instead. Again.. do they prefer one over the other? Is growth better using one over the other?
And.... at the end of the day.. is there an application of this knowledge we've come up with (preference, uptake rates perhaps, etc) to marine planted or refugia tanks?
>Sarah
Oh sure, Sarah, make me think 
You do raise some interesting points. So I'm going to sit on both sides of the fence :lol: IMO in the average tank with a planted fuge, there is likely enough HCO3- to meet the C needs of the plants. On the other hand, a tank with a heavy plant load that causes high pH problems such as yours, the use of CO2 to reduce the pH would also provide some extra C that just might enhance plant growth even more
You do raise some interesting points. So I'm going to sit on both sides of the fence :lol: IMO in the average tank with a planted fuge, there is likely enough HCO3- to meet the C needs of the plants. On the other hand, a tank with a heavy plant load that causes high pH problems such as yours, the use of CO2 to reduce the pH would also provide some extra C that just might enhance plant growth even more
Samala
New member
Mm.. right, we should make that distinction. I suppose injecting CO2 really only plays in when you have a large refugia going that needs more offsetting of pH swings or have gone to the dark side with plant-dedicated tanks.. :strooper:
Happy to muddy the waters with my questions, you should be glad you dont work with me. Around here I'm known as "little miss question mark" for all the inquisitions I make everyday.
I'd actually really like to hear Randy weigh in on alkalinity and CO2 dosing. See if there's any really complicated chemical processes I'm not paying attention to, and should.
>Sarah
Happy to muddy the waters with my questions, you should be glad you dont work with me. Around here I'm known as "little miss question mark" for all the inquisitions I make everyday.
I'd actually really like to hear Randy weigh in on alkalinity and CO2 dosing. See if there's any really complicated chemical processes I'm not paying attention to, and should.
>Sarah
I've been puzzling on how to answer this question. A large macro/grass tank, like mine, really sucks down the alkalinity readings over the course of even one or two days. Enough to warrant supplementing the alkalinity much like full blown reefs.
Unless it is a calcifying algae (like Halimeda or coralline), the macroalgae don't use up alkalinity, even if they use bicarbonate. They will leave the "alkalinity" behind as OH- as they take up CO2.
HCO3- ---> OH- + CO2
Adding or subtracting CO2 has no direct effect on alkalinity.
Unless it is a calcifying algae (like Halimeda or coralline), the macroalgae don't use up alkalinity, even if they use bicarbonate. They will leave the "alkalinity" behind as OH- as they take up CO2.
HCO3- ---> OH- + CO2
Adding or subtracting CO2 has no direct effect on alkalinity.
Samala
New member
Interesting, I guess I thought alkalinity=bicarbonate, more or less. I think I need to go read more of the chemistry articles on ReefKeeping.
So, Randy, if the plants are leaving behind the alkalinity as OH-, how come when I test for alkalinity my readings fall as the plants break apart the bicarbonate for CO2? In this tank, alkalinity falls and pH drives up if left to its own devices.
Just curious!
>Sarah
So, Randy, if the plants are leaving behind the alkalinity as OH-, how come when I test for alkalinity my readings fall as the plants break apart the bicarbonate for CO2? In this tank, alkalinity falls and pH drives up if left to its own devices.
Just curious!
>Sarah
So, Randy, if the plants are leaving behind the alkalinity as OH-, how come when I test for alkalinity my readings fall as the plants break apart the bicarbonate for CO2? In this tank, alkalinity falls and pH drives up if left to its own devices.
I don't think that most plants do use up alkalinity. Couldn't it be from other activities in the tank? This article has more info:
When Do Calcium and Alkalinity Demand Not Exactly Balance?
http://reefkeeping.com/issues/2004-12/rhf/index.htm
FWIW, some plant may well take up H2CO3 from seawater. It would be nice to have a list of those that do. Raising that may deter calcifiying organisms, but the way to do it would be to ensure that the pH was lower than normal for the alkalinity. That is, above or to the left to the left of the normal CO2 line here:
I don't think that most plants do use up alkalinity. Couldn't it be from other activities in the tank? This article has more info:
When Do Calcium and Alkalinity Demand Not Exactly Balance?
http://reefkeeping.com/issues/2004-12/rhf/index.htm
FWIW, some plant may well take up H2CO3 from seawater. It would be nice to have a list of those that do. Raising that may deter calcifiying organisms, but the way to do it would be to ensure that the pH was lower than normal for the alkalinity. That is, above or to the left to the left of the normal CO2 line here:
piercho
New member
Cattleman, the direct answer to your question is that you can use those devices sold for FW plant aquaria to lower the pH (raise the CO2) of the makeup water. Some of these depend on bacterial action, and are fairly cheap. Where you are metering in CO2 from a gas bottle, the setups are more expensive, along the lines of a reef calcium reactor.
IMO, trying to lower the pH of the FW is an inefficient method to get what you are after (more CO2 for the plants). There are more practical ways to feed CO2 to the vegetative filter than enriching your makeup water. If you are using a calcium reactor, the output will be CO2 enriched. A vegetative filter is an ideal place to have the output of the reactor go. If your veg filter is below the tank, an air drafting OF tube (like a Durso) from the tank to the filter can help "breath" the tank water. Lastly, you can route the output of a skimmer to the veg filter.
If I could offer some advice on boosting production in veg filters. The main thing to go after is to maximize nutrient advection by the plants. What is limiting? In reef tanks with adequate carbonate buffering (2.5 meq/L, or higher) and moderate pH (<8.5), IMO its rarely carbon availabilty. First the plant needs to be exposed to the nutrients you want it to take up, and it needs to breath. Route as much water flow through the filter as possible to achieve this. Keep the plants frequently pruned so that water and light easily penetrates it. Second is to provide as much light as possible. Third, use a variety of plants instead of a monoculture, no one plant has peak production potential in every tank environment. Accomplishing those three objectives will make the best use of the average veg filter, IMO and IME.
IMO, trying to lower the pH of the FW is an inefficient method to get what you are after (more CO2 for the plants). There are more practical ways to feed CO2 to the vegetative filter than enriching your makeup water. If you are using a calcium reactor, the output will be CO2 enriched. A vegetative filter is an ideal place to have the output of the reactor go. If your veg filter is below the tank, an air drafting OF tube (like a Durso) from the tank to the filter can help "breath" the tank water. Lastly, you can route the output of a skimmer to the veg filter.
If I could offer some advice on boosting production in veg filters. The main thing to go after is to maximize nutrient advection by the plants. What is limiting? In reef tanks with adequate carbonate buffering (2.5 meq/L, or higher) and moderate pH (<8.5), IMO its rarely carbon availabilty. First the plant needs to be exposed to the nutrients you want it to take up, and it needs to breath. Route as much water flow through the filter as possible to achieve this. Keep the plants frequently pruned so that water and light easily penetrates it. Second is to provide as much light as possible. Third, use a variety of plants instead of a monoculture, no one plant has peak production potential in every tank environment. Accomplishing those three objectives will make the best use of the average veg filter, IMO and IME.
Would putting the effluent from a calcium reactor raise the Co2 level in the fuge?
Yes, that is a fine idea, and likewise adding limewater to it is not.
Yes, that is a fine idea, and likewise adding limewater to it is not.
cherubfish pair
New member
Does anybody think this could work in a reef tank's refugium?
http://www.drsfostersmith.com/Product/Prod_Display.cfm?pcatid=4610&N=2004+113779
http://www.drsfostersmith.com/Product/Prod_Display.cfm?pcatid=4610&N=2004+113779
You can probably add CO2 that way (not 100% sure on its functioning in seawater, however), but the question still remains if there is any benefit to doing so.
Similar threads
