# Common signs of CO2 toxicity in fish?



## growitnow (Feb 26, 2007)

Hello,

I am still fiddling CO2 levels in my new 90gal. Pressurized CO2. It is frequent to hear comments concerning algae like "not enough CO2" (or "too much light"). This would lead folk like me who are trying to be proactive, to want to crank the CO2 up and up, even if slowly and systematically.

So, for those of you who have already done your share of fiddling, or cranked the CO2 too high and killed tank inhabitants.. maybe you can help me learn from your experience.

What are the common signs of CO2 toxicity in fish?
What behaviors might be seen? (e.g.,flashing / darting / normally bottom fish swimming in other zones)
What is the time course, how soon after CO2 is turned up?
Are some types / species of fish more likely to serve as "early indicators"?
Do fish that swim in different zones of the tank show signs first?

Thanks,
growitnow


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## newday3000 (Nov 4, 2009)

most fish will be gasping for air at the surface. I found neons were affected and Rasbors showed no signs of too much CO2


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## timwag2001 (Jul 3, 2009)

they say that fish gasp for air at the surface. never happened for me. the only sign i've ever noticed about too much co2 is death.

the best indidcator of co2 is a drop checker. you can adjust things once you get in range with that.

another good indicator is to tie down some riccia. when it starts to pearl under water, your co2 is close to being in range


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## mistergreen (Dec 9, 2006)

Get yourself a drop checker. It takes a little of the guess work out of CO2.

And fish can gasp anywhere, on the bottom, in the middle, on top. And they're stressed out easily. They can make nose dives into the substrate when frightened. Basically, when they're behaving oddly is when you're in the danger range.

Hopefully, you don't have to wait till they die to make a poisoning assessment.


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## Mr. Fisher (Mar 24, 2009)

if you use a drop checker it will not be accurate unless you use 4dkh


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## Minsc (Jul 9, 2006)

I've never seen a fish gasp from CO2. I have seen them act extremely stressed, and pass out when startled. As for shrimp, I've seen them unable to walk, and constantly fall over.


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## Momotaro (Feb 21, 2003)

> if you use a drop checker it will not be accurate unless you use 4dkh


Not necessarily true.

Drop checker will be accurate provided user knows the dkh of the solution in the drop checker and said solutions relationship to CO2 saturation level. 

4dkh is not mandatory. It is closest to the 30ppm saturation level that is most popularly maintained.


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## growitnow (Feb 26, 2007)

Good suggestions re: drop checker. I do have a drop checker (2, placed at different locations/depths of tank), with 4 dKH standard. Still interested in signs of CO2 toxicity since this is first CO2 tank. Drop checker slow to respond, human error in reading, etc. Plus since I've never had CO2 I might mistake fish behavior from too much CO2 to something else. I'd like to minimize learning the hard way


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## jreich (Feb 11, 2009)

the fish may not exactly hang out at the top but may make many frequent trips to the top for air, and will also be lethargic...


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## Kathyy (Feb 22, 2010)

Agree with the other posters, gasping. Corys react very quickly to excessive CO2 and start laying on their side, livebearers are most resistant in my tank.

If you put the drop checker in a heavy water flow it reacts much faster. I practically had ripples on the air/water interface and the pH changed within 1/2 hour.


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## ExReefer (Jan 27, 2009)

My discus would act extremely lethargic with CO2 poisoning. They would also breathe heavy (stressed) and sit upright near the bottom. I thought they were sick until I figured out I was pumping too much CO2 into my homemade PVC reactor. Those home built reactors can be extremely effective if built correctly. I had to cut my bubble rate back to ¼ of what it was prior to using the reactor.


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## Hoppy (Dec 24, 2005)

I have seen bottom dwelling fish just lay on the substrate, not moving, when I have too much CO2. My small fish seem to all cluster at the top, almost always in a corner, seemingly gasping air from the surface. And, I recall one fish type that showed a big color change, but I don't recall which one it was. Any of those are probably a sign that you need to quickly reduce the amount of CO2 you are injecting. I also recall Tom Barr telling me that bigger fish are less (more?) susceptible to CO2. Unfortunately I don't recall whether it was less or more. (Big help, huh?)


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## FSM (Jan 13, 2009)

I nearly gassed my fish a few weeks ago. The loaches were at the surface, the others (tetras and such) were much more lethargic than normal but not at the surface.


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## jreich (Feb 11, 2009)

i have notice the big fish stressing before the small fish. the big fish was a giant danio and the little fish were mostly neons and black skirt tetras.


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## growitnow (Feb 26, 2007)

This is all good feedback, many thanks. I suppose I have done a good job if I am not really that familiar with signs of fish illness. Gassing is a new possibility so more possible predictors / signals are better to know.



Hoppy said:


> I also recall Tom Barr telling me that bigger fish are less (more?) susceptible to CO2. Unfortunately I don't recall whether it was less or more. (Big help, huh?)


-- On the contrary, Hoppy. You have quite well clarified the options :icon_lol:.


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## growitnow (Feb 26, 2007)

This is a complete accident, but I was just searching for Roseline barb (Puntius denisonii) and bumped into a post of Tom's that concerned this fish -- and the relationship Hoppy mentions.



plantbrain said:


> I have 9 in a 350 gallon.
> 
> Also, the larger the fish, the more suspeptible they are to low O2 and high CO2.
> Not the other way around, ...
> ...


http://www.plantedtank.net/forums/fish/53805-roseline-sharks-puntius-denisonii.html


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## sumer (Feb 6, 2010)

drop checker will sort out your problem...
but if there is lack of oxygen in your tank first of all shrimps will be affected the will come to surface for gasping.


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## plantbrain (Dec 15, 2003)

I'd suggest everyone simply add enough good current, fish will eat better, get a work out, tank will be cleaner, *O2 will be nice and high*. Enough current just so the water's surface does not break (Hoppy's rule of Current). This does not drive off much CO2, which is very easy to add more/less of to suit, whereas O2 is much more difficult.

Without an accurate rapid method to measure CO2 and a reference to compare it against, *slow progressive adjustments* after dialing the ppm's in based on the pH/KH chart or a DC or both.....needs to be done.
This plus watching carefully your fish! CO2 needs more respect.

Do not assume that either of the two methods is accurate, it may or may not be, it will not over dose using those methods, but the risk is that it will under dose the ppm for CO2.

Adding *less intense light* also reduces the demand for CO2, and provides much more wiggle error room for dosing CO2. 


So several things can be done to make management easier this means the tank itself will be healthier for the fish and easier for you.

I do think the larger fish, like discus are excellent "CO2 canaries", with a referenced CO2 cell, we found that anythign above a CO2 of 45ppm and an O2 levels of 7ppm resulted in stress signs, namely darkened coloration and less feeding vigor, activity.

They fed and acted normally at 40ppm, even bred several times.

Tetras and most other fish and shrimp seem immune to CO2 comparatively, likely being able to handle 50-80ppm.

Poor testing methods, rapid changes, and lots of assumptions cause CO2 to be the most stickling issue. Since there's less option there with good CO2 measure, I've adopted a different approach, using less light, and it makes more sense, since this is where all growth starts.

Regards, 
Tom Barr


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## axl10 (May 31, 2010)

Hi Tom,
i added a powerhead tnite to get more circulation and the top off the water is going around in circle like motions, will i loose co2 from this. How do i tell if the water is breaking at the top. Also whats the best position for a powerhead in the tank. eg 3/4 or 1/2 way in the tank.


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## growitnow (Feb 26, 2007)

I have been thinking about Tom's indication of high O2 from a different post, and want to follow up on this - so I can better achieve it.

This seems (is?) a naive question - but many refer to "water breaking the surface" vs. not. I have a clear sense of what this means but only in the extreme case (water literally splashing, for ex: when tank water level occasionally lowers to expose output).

Can someone validate the less extreme case that we want to achieve - what does having sufficient current without breaking the surface look like?

I assume 'breaking the surface' is when one can see "bumpy ripples" in the water surface. 

And that what is desirable to minimize CO2 loss but maintain high O2 - is when you see ripples that are more gentle and less 'bumpy' (fancy language, yes?) -- but the ripples are still very clearly present.

Is this about right. Seems hard to describe.


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## Hoppy (Dec 24, 2005)

One of the reasons for having the water surface rippled is to cause CO2 loss. This may sound counter productive, but it isn't. It is easy to get more CO2 into the water, and CO2 is cheap, so increased loss from the surface isn't a big deal. But, one benefit is to lower the concentration in the water near the surface. This gives a safer area for fish to go if you do accidentally get too much in the water - fish cluster at the surface not to breathe the air by gasping it, but to get into an area with less CO2 (in my opinion - my efforts to interview those doing it haven't succeeded). In my tank, when I used CO2, the place where the fish clustered was where I knew the CO2 concentration was relatively low - a corner right by the overflow pipe, an area highly susceptible to BBA infestations. Another benefit is to increase the rate at which the CO2 is lost from the water at night, when the plants can't use it. Otherwise the concentration will temporarily tend to go up with the drop in the plants consumption of CO2.

In retrospect it now seems silly to go to such efforts to avoid killing fish with CO2, when all I really had to do was reduce the lighting, and use much less CO2. I finally reduced my lighting enough that I didn't need CO2 and got rid of the system entirely.


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## [email protected] (Oct 6, 2015)

I differ with all of you concerning CO2 Poisoning. I have killed basically all of my fish on two different occasions with what appears to be an overload of CO2. The drop checker turned yellow overnight. This happened to me in the last month. Why it is happening is still a mystery to me. Having used CO2 in my tank for over 3 years, without this happening previously makes it perplexing. Any suggestions appreciated.


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