# what fish are most tollerant of co2?



## danski (Jul 22, 2006)

i recently had an episode where all my ottos ,my rummy nose, a clown loach,and my neon died from what i believe was co2 overdose..i had a recent purchase of 10 long finned danios in there that showed no signs at all of an overdose which leads me to believe they can tollerate much higher levels of co2. my other clown loach was on his side and i couldnt see how my kuhli loaches were doing,but to me it seems that no matter what the levels these danios are super tollerant so i was wondering if theres any info on better choices of fish for a co2 tank? thanks ...dan


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## Anafranil (Mar 15, 2005)

look at a kh/ph chart and determine what your co2 is in ppm,most planted tanks 'require' around 30ppm.With that level you should be fine with all your plants and fish.I think it is not important what fish tolerates co2 more since when you are right with your consentration all all of them should be fine..


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## JanS (Apr 14, 2004)

Anafranil said:


> I think it is not important what fish tolerates co2 more since when you are right with your consentration all all of them should be fine..


That's exactly what I was going to say.


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## danski (Jul 22, 2006)

understood..so i wonder what im missing since its pretty much high-tech and i dose macros 3xs a week along with micros 2s a week and still cant find a good balance where the algae stays away. hence cranking up the co2 to try and kill it off which always works but the fish cant seem to handle it when i hit that level where the algae starts dieing. dosing E.I. for over a year and all my experimenting hasnt payed off. i use Toms suggestions on the amounts of ferts but still seems like im missing something. aaaarrgghh..

i use a drop checker and change it with a purchased 4dkh solution and fresh ph solution so im pretty sure im over 30ppm daily.. at least a visual check looks like that..im always on the light yellow side.

oh yah if i increase my ferts it seems like i get more algae contrary to everything ive been told and read. i seem to do better with a little less then reccomended..sorry i realize this is about fish so please feel free to move this if warranted.

so thats why i was wonderin about the livestock since it seems like i need to run higher levels than most for some reason and the danios had no effect at all where the others had already died. oh yah i love my fish dearly and it was a sad loss for me and my kids to lose them.


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## bigpaa (Jul 27, 2007)

Maybe you need to have some surface water movement. When does the fish expire? During lights on or lights off? When during lights off, putting an aerator during lights off hours might help.


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## BryceM (Nov 6, 2005)

I'd encourage you to start a thread about your algae issues on the appropriate part of the fourm. This has certainly given me dearly needed help from time to time.

Post your tank size, lighting hardware, photoperiod, tapwater parameters, fertilizing routine, substrate, fish load, basic plant list and a summary of the issues that you are having. There are loads of smart (and experienced) people here that will be sure to get you pointed in the right direciton.


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## danski (Jul 22, 2006)

Thank you moderator..i wasnt really looking for a solution to my algae issues here. i was trying to see what fish are the most tolerant of co2 overload which wasnt clearly answered since i swerved off that topic. i have already sought answers to all my algae issues with no solution except turning up the co2. i have followed all tips and tricks given and it still hasnt worked. my tank will balance out and stay nice for a while then falls apart even with clear and consistent routines. so i figure maybe i can have a nice beautiful tank either without fish or fish that may be a little more tollerant of co2. please feel free to close this thread if its out of line here. thank you. dan


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## BryceM (Nov 6, 2005)

nah, no worries mate! Just tryin' to help. 

I don't think there's a general consensus about which fish do poorly with high CO2. I can tell you from personal experience that I've killed corries and rainbows during my two or three CO2 mishaps. Tetras, even cardinals and rummies, seem relatively resistant. YMMV.

Don't get too frustrated by the algae. Keep after it, keep reading & learning, keep the tank as stable as possible, and you'll eventually find what works. Good luck.


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## thefishmanlives (Feb 15, 2008)

A buddy of mine gased all his fish on 3 separate occasions...all after he refilled his tank and thought he should leave the gass on high for 3 or 4 minutes to saturate the water...I mean high like 10 bubbles per second on a 55 gallon. On all three occasions he left and forgot it weas on that hi and came home to a fishocide...some of his fish actually threw themselves out of the tank


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## imaginaryrabbit (Apr 16, 2008)

I just overdosed my tank today. That killed all my cherry shrimp and 3 ottos but most of my guppies are still surviving. They are all breathing surface air. I did a water change, turned the light on, and turned the tank completely off. What a bummer!!


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## cfreeman (Mar 19, 2008)

danski said:


> i recently had an episode where all my ottos ,my rummy nose, a clown loach,and my neon died from what i believe was co2 overdose..i had a recent purchase of 10 long finned danios in there that showed no signs at all of an overdose which leads me to believe they can tollerate much higher levels of co2. my other clown loach was on his side and i couldnt see how my kuhli loaches were doing,but to me it seems that no matter what the levels these danios are super tollerant so i was wondering if theres any info on better choices of fish for a co2 tank? thanks ...dan


Hi Dan,

Awhile back I learned which fish were more tolerant of CO2 (by mishap of course). I used a calcium source which I thought would only affect GH, not KH. This was added to the tank. I had a fleeting thought of turning up the pH setting on the CO2, but unfortunately dismissed it. The pH setting was relatively low, to correspond to the value needed to maintain 30 ppm in a softwater tank. The KH was normally 2 but went up to 6 overnight, all the while the CO2 was flowing to the tank to lower the pH, which now took a lot more CO2, due to the increased KH! Looking at the pH and KH it seems that the resulting CO2 in the tank was at least 90 ppm.

Anyway, on to your question! The SAE's and Rummynose Tetras were floating. The Cardinal Tetras, Neon Tetras and Angelfish were all gasping at the surface. After water changes these three species all survived. I was pleasantly surprised to see that the Angelfish survived.

The worst part of this story ... it all happened in a friend's aquarium we were caring for while he and his family were on vacation!


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## apistomaster (May 24, 2008)

Anabantids breathe atmospheric air. They should be able to survive CO2 overdose since evolution adapted them to have the ability to live in clean but stagnant waters. 
I would work on fine tuning the CO2 use rather than changing over to bullet proof fish.


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## spcyamada (May 13, 2005)

I had this same problem with too much CO2 which killed fish and shrimp. I've yet to find a good balance between what's tolerable and not. Since starting up a new tank, I've purchased Anabantids only. They do well in high CO2. Sparkling gourami are pretty cool. I agree with apistomaster about finding the balance.


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## monkeyruler90 (Feb 27, 2008)

gouramis and all labyrith fish are great for this
they take their oxygen from the air so they wont die like the other fish. 

make sure that overdosing that co2 doesn't affect your pH too much either.

do you ahve a pressurized system or a diy?


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## cfreeman (Mar 19, 2008)

I forgot to mention that the Hatchet fish survived my episode too.

However, I fully agree with apistomaster. It is much preferable to fine tune the CO2 delivery. A pH meter linked to a solenoid on the CO2 regulator will turn off the gas once a threshold pH value is achieved.


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## Jookie (Sep 30, 2003)

Invest in a good regulator. There are some that are less reliable than others. Instead of buying fish to suit your CO2 regulator, I would buy a regulator to suit your fish needs. That's like investing in fish that can stand super high temps because your heater keeps messing up and cooking your fish.

On a side note; more CO2 = less algae has not been proven IMO. I have little algae and right now I have zero CO2 cuz I'm too lazy to get it filled across town


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## JanS (Apr 14, 2004)

Jookie said:


> Invest in a good regulator. There are some that are less reliable than others. Instead of buying fish to suit your CO2 regulator, I would buy a regulator to suit your fish needs. That's like investing in fish that can stand super high temps because your heater keeps messing up and cooking your fish.


Very good point. The addition of a pH monitor/regulator is always helpful as well.


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