# Excessive CO2 Symptoms



## Fissure (Jun 29, 2014)

Think there is no visual change in the fish and if there is it might be dependent on species etc.
What I have noticed when pushing it is fish tend to hover very close to the surface trying to use water with higher oxygen content. This is just before they actually start dying, this will not occur if the CO2 levels are just "stressfull".

Have you tested your oxygen levels in the tank, do you have good surface agitation?
And you should probably check you ammonia levels if you have fish with red gills.


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## dukydaf (Dec 27, 2004)

It depends on the species and even more on the individual fish itself. I would say otos are a good one to look after ... Only one of my otos was showing stress when reaching into 30ppm the others were fine and active. Fish will also adapt to high levels of CO2...if you add new fish to the aquarium always add way after CO2 off and before CO2, lowering the levels for a short time could also help. High CO2 is better tolerated with higher O2 levels ( colder water more surface agitation ) 

Fish can hang around the surface but they can also go to the bottom of the tank and be lethargic. If you are really over the top fish will swim erratically. Some come back if you degas fast enough.

For shrimps it depends again...randomness of nature I guess. Once I had massive fish die-off due to CO2 overdose and only a few RCS deaths. But in general they will actively swim around the aquarium, cling to plants at the surface or jump 

Fish are generally ok at 30ppm CO2 and a little higher. At one point you stop, I guess it is up to you and your aquarium priorities/status.


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## jw.cS (Jan 13, 2005)

Ammonia/Nitrite = 0 ppm
NO3 = 20-40 ppm
Temperature: <= 75F (25C) year round

4x HOB filters with gentle surface movements, NO splashing.










Water movement
https://1drv.ms/v/s!AjuZsMc6teYrgoIu67QJC8yDngKQMg

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The only thing recently that I've changed is up the CO2 a bit, just because I got these nifty drop checkers and wanted to see where my level was at all this time. I thought having 4 HOB filters would be overkill already.

All this time, I had no idea that there is such a thing as an O2 test kit at the hobbyist level. Thanks @Fissure. Found a Salifert one. Soooo, what level of O2 is recommended?

Fish (Boraras urophthalmoides, Danionella translucinda, Sundadanio axelrodi 'Blue', Corydoras pygmaeus) are not at the surface or bottom. The gills of the B. uropthalmoides are pink, not clear or red. The other fish either moves too fast or too dark for me to see their gills. Shrimps (cherries, taiwans, crs, etc.) are either clinging to floating plants or lazily grabbing near the bottom. I see a lot of cloudy bodied shrimps which concern me A LOT! Basically, maybe my paranoia is making me see everything as symptoms of impending death/stress.

@dukydaf Is 30 ppm the point where that drop checker thing turns that yellowish green color in my first post? I don't trust my eyes or what "yellowish green" or "lime green" means so I ordered the dual checker shown above. My level is not near that reference standard color contained in the inside bulb at all. It still is clearly bluish green. Maybe I should just dial it down since thst level hadn't caused me any problems in the past until I had the itch to experiment.

I was just curious what metrics other hobbyists base on to gauge CO2 level, especially when it came to the tank's fauna's behavior.


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## dukydaf (Dec 27, 2004)

I've had Boraras brigitae and the red spot was visible in the individuals that had strong coloration. I did not see a change in color at low CO2 level, but you could try and monitor it as well. 



If you only changed the CO2 and your shrimps are showing stress then reduce it and increase it at a slower pace.

Depending on the calibration of the liquid, most will turn like the green in the picture at 30ppm. Lime green is a more washed out version of that green and yellow is like this 


I like this drop checker from Dennerle because it has that white background to use use as reference. Downside is that the changes of the liquid are a bit hard to do.


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## PortalMasteryRy (Oct 16, 2012)

When you have too much CO2 the fish will have a tendency to be sluggish but it can depend on the fish. You will also see a majority of the fish hanging at the top gulping for air for about 2-3 seconds then continue on with their lives. They'll do this from time to time. Other fish sometimes get used to the conditions that they only react when you have dangerous amounts of CO2. A good example are SAE's. They seem to almost never care about my CO2 levels until they get to a point where it could kill them and I've seen it happen once with one of my tanks.

When you have dangerous amounts of CO2 then you'll fish will be constantly gulping air and they will be sort of drunk.

If you want to prevent any O2 issues then simply introduce a small air pump attached to an airstone to blow small bubbles in a corner of your tank. This will increase your O2 levels and even allow you to increase the CO2 but you will be required to increase your CO2 depending on how much air you are pumping.


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## Hoppy (Dec 24, 2005)

PortalMasteryRy said:


> If you want to prevent any O2 issues then simply introduce a small air pump attached to an airstone to blow small bubbles in a corner of your tank. This will increase your O2 levels and even allow you to increase the CO2 but you will be required to increase your CO2 depending on how much air you are pumping.


I don't think this is correct. Airstones introduce water movement, due to the rising air bubbles, but only a minute amount of that air dissolves into the water. Oxygen is much harder to dissolve into water than CO2 is. To get more oxygen in the water you need to keep the water surface rippled - both to increase the surface area and to get more water circulation at the surface. Or, you can get more oxygen in the water with a filter that exposes a large surface of water to the atmosphere, like a wet-dry filter.


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## PortalMasteryRy (Oct 16, 2012)

Hoppy said:


> I don't think this is correct. Airstones introduce water movement, due to the rising air bubbles, but only a minute amount of that air dissolves into the water. Oxygen is much harder to dissolve into water than CO2 is. To get more oxygen in the water you need to keep the water surface rippled - both to increase the surface area and to get more water circulation at the surface. Or, you can get more oxygen in the water with a filter that exposes a large surface of water to the atmosphere, like a wet-dry filter.


Well that is exactly what the small bubbles will do. It will create small ripples at the surface and that should help get more oxygen in the tank (and gas off some CO2). Since the pump is running constantly then your O2 concentrations should be a bit higher. To counter the CO2 being gassed off, you inject a bit more CO2. 

I've done this setup with 2 tanks and the only thing that stopped me from doing it was my light fixture was getting wet. I was a bit surprised how much CO2 I could inject as long as I had an airstone going. 

It's the same concept as keeping fish in a bucket with an airstone. It keeps the fish alive because it generates water movement so you have good O2 levels that keep the fish alive otherwise your fish will be dead for sure.


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## pucksr (Jan 27, 2011)

The problem with your bucket analogy is that airstones don't keep fish alive. As someone who has kept A LOT of live bait, airstones are marginal. Circulating fresh water is key. This is why most bait shops run water pumps. 

Sent from my Nexus 5X using Tapatalk


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## Axelrodi202 (Jul 29, 2008)

There are several faunal indicators. One Amano frequently mentioned is shrimp activity - if the shrimp cease to actively pick around the tank, the CO2 is likely getting to be high. A more extreme indicator is shrimp 'drunkenly' swimming around. 

If you have catfish that normally take air from the surface, their doing this more frequently than usual is an early warning sign, as is general sluggishness in all fish. More dire are fish that won't leave the surface.


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## Positron (Jul 22, 2013)

In my experience, reddish-blue gills indicate a lack of oxygen. In order of likeliness:

1)Nitrite levels too high. High nitrite impedes oxygen from binding onto red blood cells. Cuases the famous red-blue gills everytime. Can be temporary alievated by adding salt (NaCl) or using prime. 

2)CO2 very high. Too much co2 suffocates animals by decreasing oxygen absorbed per minute.

3)Low Dissolved oxygen in water. This can be caused by a few things. Dirty tanks (too much bacteria using oxygen), Very low oxygen exchange at the surface of water, a chemical that uses oxygen to do it's job (like Amquel), Too many fish and not enough surface agitation. With a fully planted tank with co2 injection at modest levels, low dissolved oxygen should never happen. 

4)A bacterial Gill disease.


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## Nordic (Nov 11, 2003)

If you find fish near drowning in CO2 treat them with methylene blue at 1 teaspoon (5ml) per 10gal. It will stain silicone, so best done in quarantine tank or tank with black silicone. The stuff is usually pretty ineffective as medicine against diseases in my opinion, but it is magic with high ammonia and low O2 sufferers.


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