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Common signs of CO2 toxicity in fish?

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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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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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Children Boogie
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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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Doesn't like Kool-Aid
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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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Discussion Starter · #8 ·
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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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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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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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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Discussion Starter · #15 ·
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.

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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Discussion Starter · #16 ·

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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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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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Discussion Starter · #20 ·
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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