Fish in a high CO2 environment (such as if your CO2 is left on overnight)

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bosoxlobsterman

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So I was perusing the site, when I noticed a thread started by Rivercats called (Accidental addition of fissidens fontanus). Now, I have no idea what fissidens fontanus is, but part of the discussion revolved around adding glutaraldehyde to the tank. Now intensely curious as to why in the world one would add glutaraldehyde to anything living ever (the only place I've used it is during a prep for electron microscopy, where you fix specimens with it and literally cross link all of the proteins), I decided to do the only natural thing. Instead of asking why you would do that, I Googled it. And was immediately sidetracked on a different forum based in India where people had been arguing about why fish don't do so well in a high CO2 environment (the protagonist was trying to convince people that it diverted the glycolosis pathway to an anaerobic state, producing alcohol. Not the case).

Long story short, the thread was shut down by a moderator with an explanation that just wasn't quite right. I've also noticed quite a bit of confusion over the subject and what exactly you can do to remedy your situation should your CO2 either be left on too high or somehow go haywire overnight so that you find some gasping fish in your tank in the morning. So I figured I could either continue studying (I'm a professional student, btw) or sit down and try to clear a bit of the confusion. I don't claim to know everything about the subject or never make mistakes, so if you have a problem with something that I say, feel free to voice an opinion. Everything here comes from getting a masters degree in an aquaculture department.

First off is the basic biology behind why we use CO2 in planted aquariums in the first place and why it's generally a good idea to turn off the CO2 at night. Plants use CO2, as well as H2O and light, to create glucose, a basic monosaccharide (think sugar), and oxygen as a byproduct. However, plants don't just sit back and make glucose for animals to come and eat them and take their energy supply. They respire just like animals and most bacteria, and take glucose and oxygen and break it down into CO2, H2O, and energy. Now, this isn't a problem during the day with CO2 because photosynthesis outproduces respiration, leading to a net intake of CO2. However, during the night, the photosynthesis pathway shuts down (no light :p) while respiration continues. This means the plants and the fish in your aquarium are both taking in oxygen, breaking down glucose, and giving off, among other things, CO2. If you are adding CO2, this means you have a bunch of extra CO2 in your aquarium, too much to offgas without building up.

Now if you don't know your chemistry (and lets face it, chemistry is a bit... tough, sometimes), CO2 in water is actually a weak acid. What this mean is that it will readily give off a free hydrogen ion (which is really just a hydrogen atom, by itself) and lower the pH in your tank. Because pH is just an inverse logarithmic scale of hydrogen ion concentration, the lower the pH in your tank, the more hydrogen ions you have. So basically if you have an excess of CO2 in your aquarium, your pH will begin to dip (depending on if/how much buffer you have in your tank).

Most fish have a natural pH range in which they can survive, but the same basic thing happens to them when they are placed in a high CO2 environment, and this is where a lot of the confusion comes into play. Most aquarium owner tend to think about a terrestrial model when thinking about this, and think that the fish have excess CO2 built up in their systems, and gasp at the surface in an attempt to ride themselves of the CO2. This is partially true. However, the underlying mechanism in fish physiology is a bit more complicated than this.

When the hydrogen ion concentration in your tank is increased, it tweaks your fish's hemoglobin in their blood. Much like people, when a fish has excess CO2 in their blood (in this case from respiration), it makes hemoglobin want to hold on to oxygen less, so that the oxygen can be released to tissues which have respired and used their oxygen. Now, this presents a problem if your dissolved CO2 is high. The hydrogen ions have the same effect on hemoglobin as CO2 (because of the chemistry used to carry CO2 on hemoglobin), so much so that it begins to affect your fish when it's outside its natural pH range.

The increased hydrogen ion concentration will literally, at some lethal point, make your fish unable to effectively absorb and carry oxygen to vital organs and the fish will die. This is true no matter how much oxygen you pump into your fish tank (in aquaculture settings its common to pump pure O2 into a system to increase the stocking capacity to increase yield; even this won't help with high CO2). The reason fish rise to the surface and try to breathe is to exchange bound CO2 with O2 from the air, which they aren't exactly good at (except labyrinth fish... they totally rock at it and are generally fine in these kind of emergencies). Unfortunately, they're still aquatic, and the hydrogen ion concentration at the surface is still far too high, preventing the hemoglobin from grabbing the O2 and getting it to where it needs to go.



So, despite having plenty of oxygen available, your fish is basically suffocating. What can you do to save him/her?? Your goal in this situation is to reduce the hydrogen ion concentration as fast as possible and return it to normal. I've been in this situation three times before (twice in my own tank, once in my advisor's tank :whistle:), and lost only one out of about three dozen fish.

First thing I always do is start as many air pumps as I have!! Why? Not for the oxygen, but to create turbulence on the surface and aid in offgasing of the CO2. Now, at home, this was the ONLY thing I did and I never lost a fish. You might not want to risk that, though. The other thing I did was an immediate water change. Not a huge amount, just 25% (although this is a fantastic excuse to do a water change that you may have been avoiding...). The only other thing you could do to help the situation in your afflicted tank is to add freshwater buffer, if you have some on hand. Buffers are designed to absorb hydrogen ions, so adding a bit extra will increase the amount of hydrogen ions your tank can handle and raise your pH (depending on the pH of your buffer).

After that, just sit back and wait. Your fish should be doing much better after a half hour or so, though you may have some deaths. Situations like this can be just as stressful for the owner as the fish, so just remember:
Grab your towel, and don't panic ;)
 
DING! DING! DING! Look at tha big brain on bosoxlobsterman!
No.. seriously tho, thanks for the info, put into layman's terms even i could understand. Cleared a few things up for me.
 
Glutaraldehyde is the active ingredient in Excel and from your obvious knowlege of chemistry you know it is used as a liquid carbon to boost plant growth.
 
Haha no probs, I had to take 4 or 5 chemistry classes before it came close to making sense... that and I get a bit argumentative sometimes :p
 
Unfortunately, your understanding of the CO2/pH/hemoglobin relationship is incorrect, but based on correct physiological concepts.

Your fundamental flaw is that you are confusing environmental pH levels with blood pH levels. As long as an organism maintains hemostatic control over its biochemistry, these two will not necessarily be related. Most higher order animals have a complex biochemical framework to prevent acidosis. You were correct about the relationship between hemoglobin CO2, but it's more complicated than you describe it. CO2 enters the bloodstream, then lowers the pH. The way you describe it is that CO2 dissolves in water, lowering the pH, which therefore lowers the blood pH, but as I previously described, the latter is not the case. If you need more proof of this, consider some blackwater fish that can survive in tannin rich waters that can often have pH levels as low as 5, well below the lethal limit of biological pHs. What is actually lethal to fish is the increase in the partial pressure of CO2 in the water. Under normal circumstances, hemoglobin releases CO2 and picks up O2 at a fish's gils according to an equilibrium that is proportional to the partial pressures of CO2 (pCO2) in the fish's blood and in the surrounding environment. Specifically, the gas exchange is directly proportional to O2 and inversely proportional to CO2 (rate = k*(pO2/pCO2) [gross oversimlification]). At pCO2 above a certain level, hemoglobin will no longer be able to properly exchange gas CO2 for O2, and the CO2 will effectively be 'stuck' on hemoglobin. The fish senses this, and goes to the surface where it expects to find a higher O2 environment (ie, higher pO2 will counteract higher pCO2).

What does this mean for your thesis statements? You best bet is to offgas as much CO2 as quickly as possible, as you correctly stated. That being said, as pH levels have little relationship with oxygen exchange, adding buffers will have no effect at all, and may worsen the fishes' shock by adding osmotic shock to the mix.
 
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Glutaraldehyde is the active ingredient in Excel and from your obvious knowlege of chemistry you know it is used as a liquid carbon to boost plant growth.

Specifically, it is thought to be a replacement intermediate in the Calvin Cycle. It is completely unrelated to true CO2 as far as tank chemistry is concerned.
 
Glutaraldehyde is the active ingredient in Excel and from your obvious knowlege of chemistry you know it is used as a liquid carbon to boost plant growth.

I was unaware that plants can use glutaraldehyde as a liquid carbon replacement, as my education was only in marine and freshwater fish aquaculture and related areas, and that is exactly why I tried to make it painfully clear that I didn't understand that bit. However, that sounded pretty cool that it can be used as a substitute in the calvin cycle, aqua chem, so I did a quick bit of research, and it would appear that what's found in Excel isn't actually glutaraldehyde, its polycycloglutaracetal, which is an trademarked isomer. These are, biochemically, two very different things and would appear to be the source of my confusion.

The other clarification I have is that pH does have a huge effect on oxygen exchange; I probably should have worded the environmental vs physiological pH part better to make everything a bit more clear.

Your bit, aqua chem, about pCO2 is absolutely correct; increasing the pCO2 level is the driving issue (the bit about blackwater fish, I would have to disagree with; clearly a pH of 5 is well within biologic tolerance for these fish otherwise the fish wouldn't survive. Calling it well below biological pH limits in that instance is a contradiction, unless you're referring to an example of environmental conditions differing from physiological conditions. In this case, I would say that blackwater fish would most likely have a modified oxygen exchange system to deal with the large osmotic pressure created between the high external H+ concentration vs the relatively low internal H+ concentration).

The actual mechanism behind the "sticking" of the CO2, however, is driven by the affinity of hemoglobin for CO2 or O2, and not by the physical pressure of the CO2. The increased pCO2 in the water column drives, through osmosis, a larger amount of "CO2" than normal into the body. However, an extremely small amount of the CO2 actually stays as CO2 (this is during any point; once the CO2 is sequestered into the water column, it pretty much reacts). The vast majority reacts with water to form carbonic acid, a weak diprotic acid. The H2CO3 then, depending on several factors, will dissociate to HCO3- and an H+ (the HCO3- can further dissociate to CO3-- and another H+) to a certain level.

Inside the blood, as there is not enough hemoglobin to sequester all of the CO2, and the end result is an increase of H+ in the blood stream itself and a change in hemoglobin affinity for oxygen (as CO2 or pCO2 increases and pH decreases, the affinity of hemoglobin for oxygen decreases). Do animals have a complicated buffering system to prevent blood acidosis due to CO2? Of course, but that doesn't mean a biological system can't be overwhelmed. In humans, blood acidosis is very apparent; just try holding your breath for as long as you can. The reduced blood pH signals your body to breath against your conscious will.

The synopsis of this is that my fundamental flaw was that I did a poor job explaining environmental vs physiological pH, not that I was confused on the subject. Adding buffers certainly would have an effect, as it would raise the pH (again, depending on what you use), though I concede that there can be osmotic issues due to the salts that are formed.

And to let everyone know, I wasn't posting this to be a smarta**, I posted because I strongly dislike misinformation, and this seems to be a topic that is riff with it. Perhaps I was astray in attempting to oversimplify a very complicated system, and especially since I may have contributed to misunderstandings, but that is why I invited a critic of the original post. And I welcome more, as well, especially to clear any more confusions :)
 
I was unaware that plants can use glutaraldehyde as a liquid carbon replacement, as my education was only in marine and freshwater fish aquaculture and related areas, and that is exactly why I tried to make it painfully clear that I didn't understand that bit. However, that sounded pretty cool that it can be used as a substitute in the calvin cycle, aqua chem, so I did a quick bit of research, and it would appear that what's found in Excel isn't actually glutaraldehyde, its polycycloglutaracetal, which is an trademarked isomer. These are, biochemically, two very different things and would appear to be the source of my confusion.

Only Seachem markets their product as polycycloglutaracetal. Other manufactures flat out say glutaraldehyde. Some people by bulk glutaraldehyde from alternate sources (such as from the medical fields) and dilute it to their needs. The thing about Seachem's claim is that it falls flat in reality. As I understand it, they were not granted a patent on it because it is, in reality, just glutaraldehyde. Acetals break down fairly rapidly in the presence of water, so you would expect almost complete reversal of the polymerization. To add to this, a while back a hobbyist with access to analytical equipment shot some Excel onto a GC-MS. The result of his analysis was that Excel was glutaraldehyde at 1.4% concentration.

Your bit, aqua chem, about pCO2 is absolutely correct; increasing the pCO2 level is the driving issue (the bit about blackwater fish, I would have to disagree with; clearly a pH of 5 is well within biologic tolerance for these fish otherwise the fish wouldn't survive. Calling it well below biological pH limits in that instance is a contradiction, unless you're referring to an example of environmental conditions differing from physiological conditions. In this case, I would say that blackwater fish would most likely have a modified oxygen exchange system to deal with the large osmotic pressure created between the high external H+ concentration vs the relatively low internal H+ concentration).
When I said below biological pH, I was referring to a circumstance where a fish was not able to properly regulate it's blood pH. I would agree that a fish in pH 5 or lower would have specialized physiological adaptations. But it follows that since the blood pH of fish is around 8, all fish would need some form of physiological defense. Animals of all kinds invest large amounts of energy in homeostasis, fish more than most. It wouldn't make sense for them to not be able to withstand reasonable ranges of pH.

The actual mechanism behind the "sticking" of the CO2, however, is driven by the affinity of hemoglobin for CO2 or O2, and not by the physical pressure of the CO2. The increased pCO2 in the water column drives, through osmosis, a larger amount of "CO2" than normal into the body. However, an extremely small amount of the CO2 actually stays as CO2 (this is during any point; once the CO2 is sequestered into the water column, it pretty much reacts). The vast majority reacts with water to form carbonic acid, a weak diprotic acid. The H2CO3 then, depending on several factors, will dissociate to HCO3- and an H+ (the HCO3- can further dissociate to CO3-- and another H+) to a certain level.

Inside the blood, as there is not enough hemoglobin to sequester all of the CO2, and the end result is an increase of H+ in the blood stream itself and a change in hemoglobin affinity for oxygen (as CO2 or pCO2 increases and pH decreases, the affinity of hemoglobin for oxygen decreases). Do animals have a complicated buffering system to prevent blood acidosis due to CO2? Of course, but that doesn't mean a biological system can't be overwhelmed. In humans, blood acidosis is very apparent; just try holding your breath for as long as you can. The reduced blood pH signals your body to breath against your conscious will.

There are two chemical reactions at work here. The conversion of CO2 to carbonic acid, and the equilibrium exchange. It's going to be clumsy to express them in text, so bare with me.

CO2/Carbonic Acid

CO2 + H2O <---> H2CO3 [H2CO3]/[CO2] = k

In this case, k is small, around .00170, making it very reactant favored. This means that vast majority of CO2 is in the dissolved gaseous phase and not the carbonic acid phase.


CO2/O2 Gas exchange

At the "gas"/hemoglobin exchange, we have the following occurring:

Hemoglobin(CO2) <---> Hemoglobin(x)
pCO2(int) <---> pCO2(ext) pCO2(ext)/pCO2(int) = k
and
Hemoglobin(x) <---> Hemoglobin (O2)
pO2(ext) <---> pO2(int) PO2(int)/pO2(ext) = k

Where x is just an open binding site on hemoglobin, ext denotes external gas levels, and int denotes atrial gas partial pressure, bound to hemoglobin.

It should be apparent that pCO2 is intimately linked to CO2 release at the gils. Assuming pCO2(ext) is constant (a good assumption), when pCO2(int) > pCO2(ext), CO2 leaves hemoglobin. When pCO2(int) =< pCO2(ext), this fails and CO2 fails to adequately leave hemoglobin. CO2 essentially becomes an inhibitor of the O2(ext) > O2(int) exchange. A lack of available binding sites causes a decrease in pO2(int), leaving the fish to slowly suffocate.

Now, does pH affect any of this? You better believe it. This is an extremely well known effect called the Bohr Effect, which basically states that in acidic environments, such as those in metabolically active tissues, hemoglobin has decreased affinity for CO2. As I understand it, this actually has very little impact on the gas exchange curve, as even with a decreased affinity for O2, the immense difference in the internal and external partial pressures (much, much greater difference than the differences in pCO2 levels) assures that hemoglobin would be completely loaded. This wouldn't make sense either, as if blood pH had an effect on gas exchange, you would be hampering your ability to uptake O2 during times of high metabolic activity/high O2 demand.

One additional point. Human homeostasis is a completely different ball game than fish homeostasis. The primary method of pH regulation is respiration, obviously not the case with fish. If I remember correctly, fish rely on H+ transporter pumps in their gils that are relatively easily modulated and adjusted, at least compared to many other homeostatic adjustments. I still maintain that fish would be able to fairly easily adjust for pH changes via this method.

The synopsis of this is that my fundamental flaw was that I did a poor job explaining environmental vs physiological pH, not that I was confused on the subject. Adding buffers certainly would have an effect, as it would raise the pH (again, depending on what you use), though I concede that there can be osmotic issues due to the salts that are formed.

And to let everyone know, I wasn't posting this to be a smarta**, I posted because I strongly dislike misinformation, and this seems to be a topic that is riff with it. Perhaps I was astray in attempting to oversimplify a very complicated system, and especially since I may have contributed to misunderstandings, but that is why I invited a critic of the original post. And I welcome more, as well, especially to clear any more confusions :)


I love it. This is my favorite type of thread on AA.
 
Thank you for the wonderful and informative discussion!!! Can I reverse gears here for minute and return to the original name of the post that references leaving CO2 on at night? As I have planted tanks but do not run CO2 systems, the answer is probably obvious to those of you that do- are you supposed run CO2 systems 24/7 or just for the duration the theres light? Is there any actual inherent danger to fish leaving a CO2 system on 24/7?
 
are you supposed run CO2 systems 24/7 or just for the duration the theres light? Is there any actual inherent danger to fish leaving a CO2 system on 24/7?
depends. If you're running co2 on a timer, it's best to run it only during the lighting period (about 30mins to an hour before it comes on and goes off). If you're running on a pH controller, it's fine to run it all night. Some people might run co2 all night without a pH controller, but that opens up the risk of killing the fish and/or inconsistent co2 levels during the day.
 
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Thanks for writing out all the bits that I hate writing, aqua chem, and for helping to clear up my post. Lack of inflection and only being able to write with simple text always makes discussions like this difficult.

Over to jlk's question about leaving CO2 on at night - mfdrookie516 is right, it really only matters if you don't have a timer or pH controller. I ran into the issue while I was first setting up my pressurized CO2 system, and I only had a beer tap regulator. It had the tendency to increase CO2 flow drastically whenever I wasn't watching. The post was intended to be part informational, part "what to do in an emergency." Precautions can always be taken to avoid issues in an aquarium, but sometime emergencies happen and you're better off knowing what to do in that situation :)
 
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