# CO2 and long term fish health



## HybridHerp (May 25, 2012)

So, I believe a few weeks back I'd been seeing in a few planted tank groups on Facebook that I frequent an article being shared around about the effects of co2 on the health of fish long term, the article I believe essentially saying that we aren't sure if longterm exposure to higher co2 levels would be bad for fish health.

Now, I know that co2 and o2 levels in the aquarium are independent of each other meaning that its possible to have both high levels of co2 for plant growth and high levels of o2 for fish respiration, but I'm wondering if the high amount of co2 in the water column can possible have effects on fish that aren't noticeable initially. I know that both o2 and co2 bind to hemoglobin in the bloodstream but would having 30ppm+ co2 end up screwing with the binding of oxygen even if there were more than ample levels of o2 (I have no idea what typical ppm values for o2 are nor do I know of any way to really test o2 levels in an aquatic environment). Is it possible that there would be other long term effects?

I'm also wondering/noticing...most of the fish people seem to keep in co2 enriched aquariums are fish on the smaller side. As I write that statement out I guess too what comes to mind are Angelfish and discus are more common examples of larger fish kept in co2 enriched aquariums...but I'm wondering if due to their larger body size if internal levels of o2 and co2 in a typical co2 pressurized aquarium would have different effects on the larger fish than it would the smaller fish (basically...being larger fish would the c02 remain in the body longer and thus cause larger fish to be more sensitive to co2 and o2 levels than smaller fish or is the size of the fish not a factor when it comes to that?).

I'm curious people's thoughts and people's evidence to support their thoughts. Idk if there exists any scientific data or anything on the long term effects of co2 on fish or anything but I'm wondering due to the sudden death of my electric blue acara (honestly it may have been from aggression...its hard for me to say though as I saw no aggression and the fish seemed to be fine on the outside but I'm unsure...perhaps something happened internally?). Its an interesting topic and definitely one to think about as to my knowledge no fish populations in the wild are subjected to the co2 concentrations that we in the planted side of the hobby sometimes keep them in. And I have a feeling there are a lot more myths about co2 and its effects on livestock than there are verifiable facts.


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## Axelrodi202 (Jun 7, 2009)

From anecdotes I've seen on monster fish enthusiast sites it does seem that larger fish (such as arowanas) are more sensitive to high CO2 levels. 

I've often thought about the issue of CO2 and fish health as well. There isn't much info out there, presumably because those who use very high CO2 levels view fish more as accessories to the plants. Personally I've noticed that most fish tend to appear to be as healthy in CO2-supplemented tanks (vibrant, well-rounded bellies) as they do in non-supplemented ones. The key is finding the limit - health declines rapidly once this has been reached/exceeded. However some species seem to be more sensitive to CO2. In my experience the only fish that has been like this are zebra otos - when I took CO2 anything beyond a very low level, they became very lethargic. Regular otos don't suffer from this.


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## Bert H (Mar 2, 2004)

Never having kept 'large fish', I can't speak for them. For my guppies, and SAE's, I haven't seen any deleterious effectsof the CO2 injection, at the levels I use, which are probably somewhat lower than the often recommended 30ppm. If you're concerned, as long as your lighting is reasonable and you're not creating a 'mini sun', dial back your co2 to 20ppm, and I would venture your plants would be fine. My 2 cents.


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