Why do we need a stable Carbon Dioxide (CO2) level?
A stable Carbon Dioxide (CO2) level or concentration is key to successfully growing plants in a CO2 injected tank. The CO2 concentration needs to be stable throughout the photoperiod, usually anything from 6 to 8 hours long, and consistent from one day to the next. If the CO2 level is not stable during this period, plants will have to constantly adapt and may not grow as well. A fluctuating CO2 concentration may also give algae an advantage and it could start to become a problem.
Stabilising CO2 during the photoperiod can be tricky and time consuming, and can sometimes take weeks of trial and error, especially for folk new to CO2 injection. Also key to success is good water flow. This is often overlooked but is essential to distribute CO2 evenly throughout the tank. CO2 travels 10,000 times slower in water than in air, so without good flow CO2 concentration will not be the same throughout the tank. Plants waving gently in the flow is a good indicator that it is adequate. Good surface agitation is also essential. This ensures adequate levels of gas exchange and helps to keep the tank water oxygenated.
What level of CO2 to aim for?
Many folk aim for a CO2 concentration of 30ppm. This is regarded as the upper safe limit for livestock. A lower CO2 concentration than 30ppm CO2 can also greatly benefit plants and is perhaps kinder to livestock, so don’t feel the need to hit the 30ppm mark. When tank water has 30ppm of CO2, the pH will be approximately 1.0 unit lower than it was before CO2 was injected. To find a tank’s CO2 level or baseline before injection starts, take a clean glass of tank water and leave it at room temp for 24 hrs after which take a pH reading. This will be the baseline or degassed pH of your tank water. For example, if the pH is 7.2 after fully degassing, and your target CO2 concentration is 30ppm then the target pH will be 6.2.
Watch your fish when Injecting CO2
It is best to adjust CO2 levels before adding any livestock to avoid accidentally stressing fish and other aquatic critters. If this is not possible it is essential to keep a close eye on your fish and shrimp etc when first injecting CO2 especially if you are new to the concept. Watch for any signs of abnormal behaviour. If the fish come to the surface and start gasping for air or show any other signs of distress, stop CO2 injection immediately. If this happens a large water change will be necessary as a temporary fix to reduce CO2 concentration and hopefully introduce more oxygen. Next check your equipment and don’t start CO2 injection again until you are confident the cause has been eliminated. If you are unable to get to the bottom of the problem seek advice or guidance, never be afraid to ask.
Injecting CO2
After starting to inject CO2 the pH of the tank water will drop quickly at first, then slowly until it reaches equilibrium with CO2 uptake by plants and CO2 loss from the water surface. If the injection rate is too high, you will overshoot your target CO2/pH which could be fatal to the tanks inhabitants so small steps at first are essential to avoid this. If the injection rate is too low, your tank water may take many hours to reach the target CO2 concentration and may not hold that concentration and remain stable once the lights come on. It’s often a case of trial and error, taking the greatest care to get it right especially when livestock is present.
Drop Checker (DC)
A drop Checker (DC) is a great tool for checking the concentration of CO2 in tank water. A working DC is filled with an indicator solution, usually a reagent in deionised water calibrated to a value of 4dkH. This solution changes colour according to the concentration of CO2. The colour will change from blue when tank water is fully degassed of CO2, to lime green when tank water has reached a CO2 concentration of 30ppm. DC’s can often change colour slowly; the rate varies with design and can take unto 2hrs. A DC can be used by itself to gauge CO2 concentration, however for the purposes of establishing a stable CO2 concentration it’s easier to use the combination of a pH profile and a DC
For further information on measurement using a drop checker, see Clive’s excellent article linked below
www.ukaps.org
Time it takes to get your target CO2 level
The time it takes to reach a CO2 concentration of 30ppm varies with tank size and injection method. About 2hrs is normal for a 50 litre tank, but bigger tanks can take 4 to 5 hours plus.
Doing a pH profile
Doing a pH profile is a great way to achieve a stable CO2 concentration and is relatively simple to do, ‘if’ a little time consuming. Firstly, decide on your target CO2 level. Then find the baseline or degassed pH of your tank water as outlined above under the heading - What level of CO2 to aim for. Set the injection rate, or Bubbles Per Second (BPS) using a bubble counter, to a suitable level for your tanks size and CO2 setup. Take the pH of the tank water as CO2 injection starts or just before.
Thereafter, take a pH reading every 30 mins and note it down. As the pH change slows down start to take the pH a little more often. If the pH drops more than 1.0 unit reduce the injection rate (BPS). If it is taking too long to get the desired pH drop increase the BPS. Once the target pH is reached, turn the lights on, then keep taking the pH every 30 mins, repeating the BPS adjustment to keep the pH as stable as possible. After 4 to 5 hours of lights on turn the CO2 off and call it a day.
Next day take the pH as CO2 comes on and thereafter every 30 mins and note the time. As the target pH is reached turn the lights on and again note the time. Some fine tuning will probably still be needed to get a stable pH (I personally call it stable when there is less than 0.1 pH drift from lights on till CO2 off). So it’s a case of ‘rinse repeat’; check the pH and adjust BPS if required to suit, until you have a stable pH from lights on and all the way through to lights off. Then the hard work is over. DO NOT adjust your BPS rate again to try and get the pH to drop faster, it is not possible. The time it takes is the time it takes. You will have already got this time noted down. It may be 2hrs it may be 4 to 5hrs with bigger tanks. The length of time a pH drop takes is always worth a final check. You will already have a rough idea from the previous days pH profiling but some further fine tuning may be required.
The whole process can take days or even weeks to perfect, especially if you need to increase the water flow to ensure adequate CO2 distribution throughout the tank, or to increase surface agitation and therefore gas exchange. Other commitments, such as work and household chores, can interfere with the process so make sure you have at least a few days free to start with, any distraction may prove fatal to fish and other aquarium livestock, again another reason why it’s best to dial CO2 in before adding livestock.
If in doubt ask
Finally, there’s no such thing as a stupid question, especially where CO2 injection and the health of fish and other livestock is concerned. So if in doubt always ask. There are many experienced and knowledgeable members who will be only too happy to help.
Zeus.
Other threads/post to read for more detail- (please post thread details of threads/post you have found useful)
Stable CO2 - What does it mean exactly? The science behind having a stable CO2 level
Using a pH controller - Pros and cons of using a pH controller to control your CO2 levels
CO2 Used data base - gives an idea of how much CO2 tanks have used
Thanks to @Guest for helping in the making of this post/summary. Special thanks to @ceg4048 ( UKAPS CO2 Guru) for all his words of wisdom and 'wit' here at UKAPS over the years. Plus to all the members who have helped me with CO2 over the years
A stable Carbon Dioxide (CO2) level or concentration is key to successfully growing plants in a CO2 injected tank. The CO2 concentration needs to be stable throughout the photoperiod, usually anything from 6 to 8 hours long, and consistent from one day to the next. If the CO2 level is not stable during this period, plants will have to constantly adapt and may not grow as well. A fluctuating CO2 concentration may also give algae an advantage and it could start to become a problem.
Stabilising CO2 during the photoperiod can be tricky and time consuming, and can sometimes take weeks of trial and error, especially for folk new to CO2 injection. Also key to success is good water flow. This is often overlooked but is essential to distribute CO2 evenly throughout the tank. CO2 travels 10,000 times slower in water than in air, so without good flow CO2 concentration will not be the same throughout the tank. Plants waving gently in the flow is a good indicator that it is adequate. Good surface agitation is also essential. This ensures adequate levels of gas exchange and helps to keep the tank water oxygenated.
What level of CO2 to aim for?
Many folk aim for a CO2 concentration of 30ppm. This is regarded as the upper safe limit for livestock. A lower CO2 concentration than 30ppm CO2 can also greatly benefit plants and is perhaps kinder to livestock, so don’t feel the need to hit the 30ppm mark. When tank water has 30ppm of CO2, the pH will be approximately 1.0 unit lower than it was before CO2 was injected. To find a tank’s CO2 level or baseline before injection starts, take a clean glass of tank water and leave it at room temp for 24 hrs after which take a pH reading. This will be the baseline or degassed pH of your tank water. For example, if the pH is 7.2 after fully degassing, and your target CO2 concentration is 30ppm then the target pH will be 6.2.
Watch your fish when Injecting CO2
It is best to adjust CO2 levels before adding any livestock to avoid accidentally stressing fish and other aquatic critters. If this is not possible it is essential to keep a close eye on your fish and shrimp etc when first injecting CO2 especially if you are new to the concept. Watch for any signs of abnormal behaviour. If the fish come to the surface and start gasping for air or show any other signs of distress, stop CO2 injection immediately. If this happens a large water change will be necessary as a temporary fix to reduce CO2 concentration and hopefully introduce more oxygen. Next check your equipment and don’t start CO2 injection again until you are confident the cause has been eliminated. If you are unable to get to the bottom of the problem seek advice or guidance, never be afraid to ask.
Injecting CO2
After starting to inject CO2 the pH of the tank water will drop quickly at first, then slowly until it reaches equilibrium with CO2 uptake by plants and CO2 loss from the water surface. If the injection rate is too high, you will overshoot your target CO2/pH which could be fatal to the tanks inhabitants so small steps at first are essential to avoid this. If the injection rate is too low, your tank water may take many hours to reach the target CO2 concentration and may not hold that concentration and remain stable once the lights come on. It’s often a case of trial and error, taking the greatest care to get it right especially when livestock is present.
Drop Checker (DC)
A drop Checker (DC) is a great tool for checking the concentration of CO2 in tank water. A working DC is filled with an indicator solution, usually a reagent in deionised water calibrated to a value of 4dkH. This solution changes colour according to the concentration of CO2. The colour will change from blue when tank water is fully degassed of CO2, to lime green when tank water has reached a CO2 concentration of 30ppm. DC’s can often change colour slowly; the rate varies with design and can take unto 2hrs. A DC can be used by itself to gauge CO2 concentration, however for the purposes of establishing a stable CO2 concentration it’s easier to use the combination of a pH profile and a DC
For further information on measurement using a drop checker, see Clive’s excellent article linked below
CO2 Measurement Using A Drop Checker
www.ukaps.org
Time it takes to get your target CO2 level
The time it takes to reach a CO2 concentration of 30ppm varies with tank size and injection method. About 2hrs is normal for a 50 litre tank, but bigger tanks can take 4 to 5 hours plus.
Doing a pH profile
Doing a pH profile is a great way to achieve a stable CO2 concentration and is relatively simple to do, ‘if’ a little time consuming. Firstly, decide on your target CO2 level. Then find the baseline or degassed pH of your tank water as outlined above under the heading - What level of CO2 to aim for. Set the injection rate, or Bubbles Per Second (BPS) using a bubble counter, to a suitable level for your tanks size and CO2 setup. Take the pH of the tank water as CO2 injection starts or just before.
Thereafter, take a pH reading every 30 mins and note it down. As the pH change slows down start to take the pH a little more often. If the pH drops more than 1.0 unit reduce the injection rate (BPS). If it is taking too long to get the desired pH drop increase the BPS. Once the target pH is reached, turn the lights on, then keep taking the pH every 30 mins, repeating the BPS adjustment to keep the pH as stable as possible. After 4 to 5 hours of lights on turn the CO2 off and call it a day.
Next day take the pH as CO2 comes on and thereafter every 30 mins and note the time. As the target pH is reached turn the lights on and again note the time. Some fine tuning will probably still be needed to get a stable pH (I personally call it stable when there is less than 0.1 pH drift from lights on till CO2 off). So it’s a case of ‘rinse repeat’; check the pH and adjust BPS if required to suit, until you have a stable pH from lights on and all the way through to lights off. Then the hard work is over. DO NOT adjust your BPS rate again to try and get the pH to drop faster, it is not possible. The time it takes is the time it takes. You will have already got this time noted down. It may be 2hrs it may be 4 to 5hrs with bigger tanks. The length of time a pH drop takes is always worth a final check. You will already have a rough idea from the previous days pH profiling but some further fine tuning may be required.
The whole process can take days or even weeks to perfect, especially if you need to increase the water flow to ensure adequate CO2 distribution throughout the tank, or to increase surface agitation and therefore gas exchange. Other commitments, such as work and household chores, can interfere with the process so make sure you have at least a few days free to start with, any distraction may prove fatal to fish and other aquarium livestock, again another reason why it’s best to dial CO2 in before adding livestock.
If in doubt ask
Finally, there’s no such thing as a stupid question, especially where CO2 injection and the health of fish and other livestock is concerned. So if in doubt always ask. There are many experienced and knowledgeable members who will be only too happy to help.
Zeus.
Other threads/post to read for more detail- (please post thread details of threads/post you have found useful)
Stable CO2 - What does it mean exactly? The science behind having a stable CO2 level
Using a pH controller - Pros and cons of using a pH controller to control your CO2 levels
CO2 Used data base - gives an idea of how much CO2 tanks have used
Thanks to @Guest for helping in the making of this post/summary. Special thanks to @ceg4048 ( UKAPS CO2 Guru) for all his words of wisdom and 'wit' here at UKAPS over the years. Plus to all the members who have helped me with CO2 over the years
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