bosoxlobsterman
Aquarium Advice Activist
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 ) 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 ), 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
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 ) 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 ), 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