# What happens when you add too much Co2?



## JerseyScape (Nov 18, 2005)

Besides wasting the gas, what are some other ill-effects of injecting too much Co2? (let's say the tank would have no fish or no shrimp).

I know that after a certain point it becomes useless to inject more but does it actually hurt plants?

Thanks


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## Zapins (Jul 28, 2004)

Not in my experience. it seems more co2 virtually wont ever hurt the plants. consider that most of our aquatic plants can live in the open air via emersed growth. the air contains far higher concentrations of co2 then our water ever could so there is no reason to believe that they would suffer any damage from high co2 levels underwater... 

Some other observations:
I keep my levels between 200 and 300 ppm as I have found this reduces the spread of algae.

It is actually possible to keep fish/inverts in these high co2 conditions i keep 4 cardinal tetras and 1 ottocat in my 55 gal tank and about 30 cherry shrimp//snails. you will have to acclimatize your livestock slowly though over a period of a few days//weeks. 

Though fish and shrimp seem to respond well to this sort of conditioning, snails don’t. their shells become increasingly pocked as the carbonic acid in the water eats away their calcium shells.

But regardless, having high co2 is helpful in many aspects and i would encourage it if you can get to those levels.

In addition, it actually isn’t very wasteful to inject high levels of co2 into the aquarium, as long as you have an efficient setup. For example, an inline co2 reactor will give you nearly 100% efficiency with dissolving co2 into the water, and specially designed co2 resistant tubing will only lose around 2% of all the gas passing through it per foot. So if your co2 tank is next to your filter/diffuser then you will need no more then 1 foot and will be able to convert 98% of the total co2 leaving your co2 bottle into useable co2 for your plants. 
Just for reference silicon tubing leaks 20-30% of all the co2 passing through it per foot. Its basically useless to use silicon as you will be wasting 30% of your entire co2 tank over the course of its life.


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## BryceM (Nov 6, 2005)

Hmmmm,

I don't agree with everything that Zapins had to say. The concentration of CO2 in air is about 3 ppm or 0.03%. This is exactly the same as it is in water that has been allowed to come to equilibrium (outgassed). That said, if you're not intending on keeping fish or inverts, then the plants can tollerate a healthy dose. At some point though, more CO2 really drops the pH. Once you get down too low many of the enzymes that plants rely on cease to function real well. Some plants do better than others.

Most people that claim to have high CO2 readings are being 'tricked' by large concentrations of other organic acids in the water or by other buffering systems that they aren't aware of. Errors in CO2 measurement almost always cause you to overestimate the real value, sometimes by as much as 4X.

At a certain point more CO2 doesn't help any more than more NO3 or more PO4 would. The plants do have a maximum capacity to assimilate and grow. You can't 'force feed' them. The best you can do is to supply a balanced array of nutrients at the exact same rate the plants are using them. Overdosing on one thing won't make much difference.


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## Zapins (Jul 28, 2004)

Actually the air contains anywhere from 350ppm and upwards depending on whether you are indoors or in a closed off space or near a city etc... but 350 is the average ppm in the air today not 3 ppm. 

I do agree with your statement of plants being inhibited by lower pH value but this does not necessarily have to happen since you can dose KH accordingly and keep the water's pH around 6 rather then into the lower numbers, thus avoiding enzymatic damage while still increasing the water's saturation of co2.

While I am sure my measurements are not 100% accurate or even close to that. I am quite sure that they are high enough to kill a fish that has not been acclimated over a long period of time if put in quickly. this puts me well over 30ppm threshold that some propose is lethal. I observed the fish gasping and seemingly starting to pass out when I was acclimatizing my new batch of 8 tetras to my tank with not even 2 cups of tank water to the bag (about 30% of total bag water). They were all at the top gasping, while the same species of fish that I bought and slowly acclimatized over long periods of time were diligently swimming around the bag waiting to meet the newcomers.

The process by which fish acclimatize to more co2 in the tank is not very difficult to imagine since the problem that causes death is clear. Fish die of suffocation like a human would if there were too much carbon dioxide in the air. however there are ways around this problem biologically. For instance producing more red blood cells to carry more of the available O2 around the body, and also an increase in buffering of the blood to compensate for more co2 present there.

Also, as for force feeding plants co2. You are correct you cant force feed them more then their metabolism allows and the other nutrients in the tank allow. I suggested he may have it easier keeping very high levels of co2 since it seems to limit certain algae species from growing rapidly as Tom Barr has repeatedly told us all.


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## BryceM (Nov 6, 2005)

Ah, Zapins, methinks you might have a point. My confusion stems from the fact that a dissolved gas will have the same partial pressure in a liquid as it does in the atmosphere above the liquid if allowed to come to equilibrium. Atmospheric CO2 is about 350 ppm +/-. Dissolved CO2 in water is about 3 ppm.

I will stand by my claim though, that there is not "more" CO2 in the atmosphere than dissoved in water. Water is much, much more dense than air (big revelation huh?). The same quantity (or mass) of CO2 in air will have a much higher concentration than the same quantity of CO2 dissolved in water since the denomonator is bigger.

As if it weren't confusing enough already......


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## locus (Dec 7, 2004)

Too much CO2 makes my Glossostigma very leggy, and it doesn't seem to send roots into the gravel very well either. I spent ages scratching my head as to why my glosso wouldn't stay low, then one day my CO2 ran out... now I try and keep my CO2 levels quite a bit lower (not sure of PPM, I just watch the plants).

I've also noticed that my cardinal tetras become shy and less active with too much CO2 (no gasping though).


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## Zapins (Jul 28, 2004)

Hehe, yup guaiac.

JerseyScape: that is very interesting since i noticed something similar. I thought the glosso's leggyness was due to the new bulbs i bought off ebay being of lower quality. But i didnt think it might be too much co2... As for the cardinals, i noticed mine have been hiding too, but i thought it was from there being only 4 left in a huge 55 gal tank. Hmmm i think i will lower the co2 concentration and see if things improve.


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