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Anyone have suggestions for small, CO2 resistant fish? I have a nice group of 50+ CPD's that seem to tolerate a high level of CO2, but of course I only ever see them at feeding time. None of the other species I tried seemed nearly as tolerant, and I really hate to turn down the CO2.
 

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It's not really the CO2 you need to worry about, it's the oxygen content of the water. Water saturated with CO2 = low to no oxygen. Fish need oxygen to live, much like humans do. Filtering water over their gills that has no oxygen in it is essentially suffocating. Keep the oxygen content good and you can supply good CO2. Things like surface film and inadequate circulation lead to oxygen deficiencies.
 

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Water saturated with CO2 = low to no oxygen. Fish need oxygen to live, much like humans do.
This is not true.

Injecting CO2 and saturating water with it will not drive oxygen out from the water.

Rather, it is the high concentration of CO2 that kills fish; the amount of oxygen in the water will remain relatively stable. Diffusion of CO2 from the bloodstream across the gills (respiration) is dependent on CO2 concentration differences; in high CO2 levels, the amount of CO2 that be diffused out from the fish is lower, meaning that they can suffocate.
 

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Gouramis are also Labyrinth fish, as well as the many Badis fish and sub/cousin species Dario Dario (which is just TOO DARN CUTE).

Betta's are really cool though, and very under-appreciated. Females can be kept together in large groups called Sororities, and because of the many colors, sizes, and tail types, you can create a veritable rainbow of color in your tank. Unlike the typical schooling fish people like to keep, which are essentially pretty decorations, betta are very intelligent and interactive, each having their own individual personalities, giving you a chance to actually feel like your fish are proper pets!
I have a 4 girl sorority right now in planted ten gallon, and watching my girls is one of my favorite things to do as I decipher their pecking order and the alliances and rivalries that emerge between them :]
 

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This is not true.

Injecting CO2 and saturating water with it will not drive oxygen out from the water.

Rather, it is the high concentration of CO2 that kills fish; the amount of oxygen in the water will remain relatively stable. Diffusion of CO2 from the bloodstream across the gills (respiration) is dependent on CO2 concentration differences; in high CO2 levels, the amount of CO2 that be diffused out from the fish is lower, meaning that they can suffocate.
This is a very interesting concept. Thanks for your post!
 

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This is not true.

Injecting CO2 and saturating water with it will not drive oxygen out from the water.

Rather, it is the high concentration of CO2 that kills fish; the amount of oxygen in the water will remain relatively stable.
This is not true.

While you're correct that CO2 does not displace oxygen, the actual oxygen levels can vary significantly depending on how many plants are photosynthesizing and giving off oxygen in the process. A well balanced planted tank with CO2 injected will actually have INCREASED O2 levels due to this.

Whether or not the increased CO2 and O2 levels can suffocate fish is something I don't definitely know about, but I know that I've seen some pretty happy fish in tanks with increased CO2 and O2! Perhaps eventually the increased CO2 will have an effect, but I don't think that would be common with the levels we're normally talking about.
 

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This is not true.

While you're correct that CO2 does not displace oxygen, the actual oxygen levels can vary significantly depending on how many plants are photosynthesizing and giving off oxygen in the process. A well balanced planted tank with CO2 injected will actually have INCREASED O2 levels due to this.

Whether or not the increased CO2 and O2 levels can suffocate fish is something I don't definitely know about, but I know that I've seen some pretty happy fish in tanks with increased CO2 and O2! Perhaps eventually the increased CO2 will have an effect, but I don't think that would be common with the levels we're normally talking about.
just lost a ton of fish due to a CO2 malfunction yesterday. they gasp at the surface, as if there were low O2, because the body does not measure O2. the body tells you that you need air when your medulla (part of the brain) detects high levels of CO2, since [CO2] and [O2] are inversely proportional in the body.
however if you dump CO2 in the tank, the fish will die even if there is tons of O2, as CO2 is poisonous. it has narcotic effects. it is an approved means of veterinary euthanasia.
 

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just lost a ton of fish due to a CO2 malfunction yesterday. they gasp at the surface, as if there were low O2, because the body does not measure O2. the body tells you that you need air when your medulla (part of the brain) detects high levels of CO2, since [CO2] and [O2] are inversely proportional in the body.
however if you dump CO2 in the tank, the fish will die even if there is tons of O2, as CO2 is poisonous. it has narcotic effects. it is an approved means of veterinary euthanasia.
That makes sense. I thought we were talking about CO2 levels that we purposely are injecting into our tanks, though. Those will actually increase O2 levels in the tank.
 

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This is not true.

While you're correct that CO2 does not displace oxygen, the actual oxygen levels can vary significantly depending on how many plants are photosynthesizing and giving off oxygen in the process. A well balanced planted tank with CO2 injected will actually have INCREASED O2 levels due to this.

Whether or not the increased CO2 and O2 levels can suffocate fish is something I don't definitely know about, but I know that I've seen some pretty happy fish in tanks with increased CO2 and O2! Perhaps eventually the increased CO2 will have an effect, but I don't think that would be common with the levels we're normally talking about.
That makes sense. I thought we were talking about CO2 levels that we purposely are injecting into our tanks, though. Those will actually increase O2 levels in the tank.
Yes, I am aware that oxygen levels can actually be higher than saturation in the aquarium given a well planted aquarium (i.e. this is why pearling occurs).

just lost a ton of fish due to a CO2 malfunction yesterday. they gasp at the surface, as if there were low O2, because the body does not measure O2. the body tells you that you need air when your medulla (part of the brain) detects high levels of CO2, since [CO2] and [O2] are inversely proportional in the body.
however if you dump CO2 in the tank, the fish will die even if there is tons of O2, as CO2 is poisonous. it has narcotic effects. it is an approved means of veterinary euthanasia.
Correct, at least in human physiology (not sure about piscine physiology). The body measures concentrations of CO2 and that drives the need to respire. If you hyperventilate before diving, you drive out excess CO2, and thus can theoretically dive for a longer period of time, since you trick your body into believing it does not need to respire. However, this is dangerous, since it is possible to run out of oxygen before you even feel the need to respire (i.e. you will pass out from lack of oxygen without feeling the need to respire).
 

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fish respirate different than humans, in such that they are FAR more efficient than we are..
while co2 does play a crucial role, it affects them much less than it does us.
Oxygen concentrations control, to a certain extent, how much co2 any given fish can tolerate. some fish will handle it better than others

increasing oxygen levels will effectively raise the tolerance limit on any given fish. the tolerance level will be determined by the fish of course.

i run a super yellow Drop Checker ( this is for reference) and my ph drops 1.6 degrees from when i turn on co2.. so i inject quite a bit of co2, i run a wet/dry filter to increase oxygenation
and my fish spawn frequently to prove they aren't stressed. my rainbows spawn pretty much bi weekly, i have 3 males and 4 females at this point and thee pretty much rotate spawns

otto's try often, and my tetra's well it happens, but all the eggs get eaten by loaches
 

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Fish gills are much, much more efficient than our lungs are.

I think too much CO2 doesn't remove the O2 but it limits the ability for the fish to expunge CO2 in their body into the environment. It's akin to the Apollo 13 CO2 scrubbing problem.
 

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Actually Darkblade48 was spot on.... in-ability to offload CO2 at the gills, drops blood pH, which triggers the fish to behave as if it were deprived of O2. Eventually the fish goes into shock, at which point it's incapacitated, therefore a hot dose of CO2 can be used for anesthesia, but be warned, the knock down process is not a pleasant one for the fish-i.e. not very humane method. If removed from the high CO2 conditions in a few minutes the fish can rapidly recover.

When you see fish that appear healthier in a planted thank with CO2, it's probably just due to the O2 supersaturation than any CO2 content (or perhaps they are low pH fish that are happier in due to lowered pH). The higher the D.O. the less the fish has to pump it's gills, the more active they can be with out having to rest.

Now I don't believe subjecting labyrinth fish to high CO2 content will be anything short of a torture experiment. Their adaptation is to take in air to their labyrinth organ to take in oxygen, they are still pumping their gills in the low D.O. water to offload CO2-which they wouldn't be able to do and would share the same fate as the rest of the fish. All that being said, if your drop checker is yellow, but your fish are not up at the surface gasping in the morning(assuming you ran co2 all night) then your levels are fine, but as soon as that solenoid sticks, kiss your babies good bye. Also mind the GH/KH of your water, and the pH swings as that will do in some species as much as anything.

This is not true.

While you're correct that CO2 does not displace oxygen, the actual oxygen levels can vary significantly depending on how many plants are photosynthesizing and giving off oxygen in the process. A well balanced planted tank with CO2 injected will actually have INCREASED O2 levels due to this.

Whether or not the increased CO2 and O2 levels can suffocate fish is something I don't definitely know about, but I know that I've seen some pretty happy fish in tanks with increased CO2 and O2! Perhaps eventually the increased CO2 will have an effect, but I don't think that would be common with the levels we're normally talking about.
 
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