co2 for plants
 

So, I was reading an old thread about making your own co2 diffuser. It said to just stuff some cotton or a chopstick in the end of an airpump to creatte the tiny bubbles. But then, they were talking about how to make the co2 mixture (using sugar or something). So what I don't get is why do you need a special mixture to give your plants? Doesn't regular air have lots of co2 in it? Wouldn't it have the same effect if you just used an air pump and diffuser?
Thanks!

No, if you run air through a bubbler of any sort it drives excess dissolved CO2 out of the water. The plant leaves don't absorb CO2 under water nearly as well as in air which is partly why some do this. If you want to add CO2, you actually have to add compressed CO2 either using a DIY method or a compressed CO2 through a regulator and some sort of bubbler. Even just additional surface disturbance will drive CO2 out.

Too complicated for me to bother with. I figure if I can't grow plants underwater adding more complication is not going to make it any easier.

Jeff.

I'm actually ready to try out diffusing atmospheric air in tank water. Theoretically it should work. and if it does, it's a lot cheaper than a CO2 setup and doing refills.

like I was trying to explain to someone before atmospheric air (especially in a room) can have up to 3000ppm of CO2....

Ouch, if your CO2 levels in your room are that high, I'd be more worried about getting some air exchange in there. Normal atmosphere is somewhere under 600 ppm and over 1000ppm can start to cause issues for the people, not major at that level but still, long term not great. Any sort of air exchange will keep it down normally anyway.

Water is somewhere under or around 10ppm CO2. Consider that if you put tap water into a jar and shake it, the CO2 is removed from solution to it's equilibrium point of under 10ppm. Given that air may be at 500ppm and tap water at maybe 20ppm, this leads me to believe that CO2 really does not "like" being dissolved in water so running air through the water would remove the CO2 from solution as it serves the same purpose as shaking the tank.

Running air will not imbue the water with more CO2, quite the reverse.

For the fish, the higher the CO2 the less efficient they are at absorbing O2 in the water, you can overdo it with compressed CO2 and, particularly at night when the plants are not producing O2 but are producing CO2, you could suffocate the fish... worst case scenario.

Jeff.

Jeff, you mentioned something I had not thought of, with the out-gassing CO2 by agitating the water. This would seem to substantiate the still-prevailing view that any water disturbance is not going to bring CO2 into the water but the reverse.

The level of CO2 in a natural lanted tank is certainly higher than in the air, due to the breakdown of organics which is the main source. So any bubbling to allegedly bring CO2 from the air into the tank will have the opposite effect.

Byron.

Yes, and no. It seems counter intuitive that such a discrepancy in concentrations would not automatically transfer from the higher to the lower but water and air contain CO2 in different manners so they cannot be compared one level vs the other. Even in a planted tank with CO2 being injected the level in the water is still going to be more than 25 times lower than in air based solely on a ppm measure (not sure if going by volume or weight make much of a difference in this comparison).

CO2 comes out of solution and is absorbed by air many times easier than the reverse so there is a certain equilibrium reached between the two. When plants off gas CO2 or it is injected, it raises the water CO2 content above that of the equilibrium at the surface of the water. Moving the water increases the transfer just like shaking the jar for the tap water test. Ground or tap water has a higher concentration of CO2 than still water probably due to not being exposed to air.

pH affects how much CO2 the water can contain... conversely adding CO2 alters the pH but the water will attempt to return to it's natural pH... I'm sure you've seen this... so even the water will fight to push the CO2 out to return to it's equilibrium pH.

I am finding that there is so many inter-related equilibriums going on in water that messing with one thing has so many implications across the entire chemistry that I would rather just use the water in it's natural form right from the tap and let everything stabilize as it will.... including the CO2 levels.

Jeff.

I did not mention bubbling, but rather diffusing atmospheric air into the tank with the use of an atomiser or diffuser. it's fun to work with theories, but until someone tries this, there's no need to reject it :) I myself believe that it will create an environment closer to that of an emmersed set up and promote plant growth.

I often consider situations sans fish, as I myself have fishless tanks. if we start to talk about atomized air interfering with the gills or other bodily functions of fish, that's a whole other different issue.

3000ppm will make a person sleepy, but nothing terrible will happen. It's not that rare for levels to be that high in a crowded room.

I know, but 3000 for extended periods of time indicates an air exchange issue and, long term, can cause more than sleepiness. I doubt the tank is going to be in a crowded room. There is a working standard somewhere that mentions 8 hour shifts in levels of 5000 ppm in closed environments as the maximum allowed based on some health and safety study.

Atomizer, diffuser, just smaller bubbles. If moving the surface of the water causes CO2 to diffuse from the water quicker than still water, already proven by experiment, not a theory, done it myself, and all a bubbler, atomizer, diffuser does is disturb the water from below, then all you are going to do is change how you are disturbing the water and not introducing anything new to the experiment that will change the general result.

It might be interesting to see, by creating smaller bubbles and therefore increasing area of the air/water exchange surface, how much faster or how much more CO2 will be removed from the water.

Jeff.

I've never seen a CO2 diffuser that creates significant turbulance. The flow should not be allowed to be that great either. If CO2 diffuser created water distubance, it will defeat the purpose of CO2 injection and prove to be counter productive....

The scenario is basically replacing a CO2 tank with something like an airpump and a control valve that brings in atmospheric air at a controlled rate...

does that make more sense or are you still thinking airpumps, airstones and lots of water movement?
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