# How many CO2 bubbles per gallon of water?



## bms

I just setup my DIY CO2 system using soda bottles... I have no clue if the CO2 I am inyecting is to much or to little.

I have a 20 gallon tank.

Is there anyway to aproximate the required number of bubbles that need to go in the tank (assuming 100% disolution) to reach an acceptable CO2 level?

I am currently getting a bubble every 3 to 4 seconds.... does that seem right?


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## Sir_BlackhOle

I dont know of any standard "bubbles per gallon" rule. I think what you will have to do is measure your KH and pH and use the co2 chart to find out how much co2 your are actually getting. I think a good range is 20-30 ppm. Someone please correct me if I am wrong. You can find the co2 chart here http://www.thekrib.com/Plants/CO2/kh-ph-co2-chart.html

On my diy co2, when fresh, i get a bubble every 2 or 3 seconds.


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## Steve Pituch

Right on Kevin,

It would also be interesting to use the chart to see how much CO2 is in the water before injection. It only may be a couple of ppm. Even if you got it to 15 ppm it probably would be helpful.

Steve


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## bms

Well I guess my CO2 is on normal range... difference may be due to different mix (I am using about 1.5 litters of water, 3/4 cup of sugar and one tablespoon of yeast.)

How big is your tank?


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## bms

I mean the CO2 production of my DIY CO2 is what was expected... still have to check the water PH to see if it is OK.


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## Moss

Hi. Some of us in Portugal use the following formula:

*liters x 13 / 100 = number of bubbles per minute*

so in my 120l tank I should have about 15 or 16 bubbles a minute.

(1 gallon = 3.785 liters US or 4.546 liters, British Imperial System) 
I don't know how accurate this formula is, though...:roll:

Regards.


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## bms

This comes to about 1 bubble every seconds... so according to this formula I may be adding to much CO2.

I believe however that this is only a guideline... I would presume the number of plants and fish in the tank will play a role in how much CO2 you need and ultimately in how much you need to inject.


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## Moss

Sure. And also if you have a reactor or if you just let the bubbles come out directly from the tube into the water (less effective). Just be careful, use the chart and keep in mind that drastic Ph changes can kill the fish. 
Regards.


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## gpodio

Bubbles per second are really only useful for knowing when there has been a change in CO2 output or to set the bubble rate to where it used to be after having played around with it. It says nothing about your CO2 levels in the tank.

There are too many variables to use bubbles per minute effectively, it's like saying that 10 gallons of gas will get you 100 miles of travel without considering the driving conditions, engine size and weight carried.....

Here are some variables you need to consider:

- If you use a less than perfect method for diffusing CO2, you will need more bubble per minute to maintain the same level of CO2

- CO2 is easily lost due to gas exchange. The amount of gas exchange occuring in your tank will depend mostly on the amount of surface agitation created by your filter's return.

- Temperature of your water will dictate how much dissolved gases it can hold and the ease at which CO2 is dissolved into the water.

- Plant uptake will also play a minimal role in determining how much CO2 il left in the water.

So as you can see, running 10 bubbles per second through an air stone is probably going to give you less CO2 concentration than 1 bubble per second through a powered reactor. Infact in my opinion, controlling surface agitation and diffusion efficiency is the best way to control CO2 levels for DIY setups where CO2 output can not be adjusted.

In conclusion, measure your KH and PH, then use the table to know how much CO2 you have. Once you reach the desired amount, you can note how many bubbles per minute are required for YOUR tank to maintain such level. Should you change the amount of surface agitation or method of diffusing CO2, you will need to re-calculate your required bubbles per minute.

Here's a short article I wrote on DIY CO2, hope it can help
http://www.gpodio.com/diy_co2.asp

This is one of those cases where you "bubble milage" will certainly vary from others...

Hope that helps
Giancarlo Podio


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## Moss

Hi. Giancarlo your article is very helpful, specially for newbies like myself. For instance, I always changed the amount of sugar, thinking it would be more effective (I'll stop doing that). By the way I always use baking soda in my mixture. I was told it doesn't "allow" drastic Ph changes. In fact, values remain stable with baking soda. Have you got any input on this?
Thanks. 
Regards.

By the way, I like your final advice.


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## Corigan

Baking soda is also supposed to make the mixture last longer. I always put baking soda in my mixtures as well.

Matt


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## Sir_BlackhOle

Baking soda? Thats one I havent heard before. I have been using 2 cups of sugar and 1/2 tsp yeast in a 2 liter bottle. How much baking soda do you add?


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## dennis

Generally aabout the same amount of baking soda as yeast works well for me. The baking soda seems to slow down the reaction adn it also raises the kH( and thus the pH) of hte mix so the yeast can work longer before it gets to acidic and kills the plants. My mixes generally last 3 weeks before replacing. I am also trying something new. Check out my thread in the DIY section "DIY Pressurized CO2". Just use at your own risk. I make no promises or claims. Works well for me though.


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## bms

There are a lot of recepies out there for the mix... I am currently using 3/4 of a cup of sugar, 1 tsp of yeast on roughly 1 liter of water. Does that sound OK?

In regards to adding baking soda to the mix, if I understand correctly the BS will increase the production of CO2, therefore making it necessary to add something to control the preassure on the bottle and the amount of CO2 delivered to the tank. Is this correct or does it only make the reaction last longer withouth increasing the production of CO2 at a given time?


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## gpodio

dennis said:


> The baking soda seems to slow down the reaction adn it also raises the kH( and thus the pH) of hte mix so the yeast can work longer before it gets to acidic and kills the plants.


I think you meant to say before it kills the yeast.

In general, CO2 production from a DIY setup will be quite high at first and then slowly taper off as the days go by. This makes it hard to maintain a constant CO2 level and people need to resort to tricks such as pushing the micro bubbler (if you use one) deeper and deeper each day to increase the amount of CO2 that is diffused as the rate of production drops. Baking Soda seems to even things out and provide a more stable CO2 production throughout the lifetime of the bottle. A more effective method, yet more work involved, is to use a Jello mixture. The jello makes the sugar available to the yeast a little at a time, therefore maintaining a more stable CO2 output. In this case, the amount of water used is very little so you often need to tip the water out, add some more with some fresh yeast until all the jello is consumed.

Giancarlo Podio


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## bms

Giancarlo,

Jello... interesting, could you comment on the specifics of the "recepie" for the mix you use or have used and your personal experiences with it?

Thanks!
~Benicio


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## gpodio

I only used this a couple times to see how it works, in the end however I needed as much CO2 as I could get so I ended up using the traditional method without any kind of stabalizer.

The jello bottle:

- Prepare some jello following regular recipe on the back of the box
- avoid eating it :wink: 
- pour the liquid into the bottle and place it in the fridge as the instructions tell you to do
- once it's hardened, activate some yeast in warm water and pour it in the bottle
- The more water you add the better as it will quickly turn to alcohol and spoil the yeast
- when the yeast is dead after a few days, simply tip the water out and add some more water and yeast until all the jello is all consumed, then start all over again

I think it works best for smaller tanks where you don't need all the CO2 produced by a traditional 2lt bottle, it produces less CO2 but it's stable and lasts longer.

Someone posted a much better description once... somewhere, if I find it I'll copy it here.

Hope that helps
Giancarlo Podio


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## bms

did a search on google and came up with this:



> - Add 2 packs of regular jello, not the light stuff, to an empty and clean 2l pop bottle.
> - Add boiling water to dissolve the jello
> - Add your 1-2 cups of sugar
> - Add enough water to fill the bottle to about 1.5l
> Store in the fridge overnight to let the jello set.
> On the following day:
> - Add 1 cup of water and the yeast (1/8 teaspoon) on top of the jello. Attach your bottle as normal."


I am going to try it out. I read somewhere else that one needs one of these bottles for every 30 gallons of water.


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## gpodio

Again, it depends on your efficiency of diffusion and loss. I was able to run my 55 gallon tank on a single bottle, but I had no surface agitation and 100% diffusion rate.

Giancarlo Podio


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## bms

OK guys... I had not seen the table until today (I did not have a way of measuring PH).... now I measured my PH it is at 7.0 but have no way of measuring my KH... do I need a test kit for that?

I had my water tested yesterday at my LFS.. they said it was to hard and told me to ad salt... does this have anything to do with KH levels?


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## Sir_BlackhOle

Yes you need a test kit to measure KH, or you can ask your LFS to test your water and tell you what it is. I'm not too sure I would follow their advice about it being too hard.


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## bms

Does KH stand for anything?, they tested it for Chlorine, Nitrate, Amonia, Hardness, and PH yesterday.


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## Sir_BlackhOle

There are two types of hardness, GH-general hardness, and KH-carbonate hardness. KH is what you want for determining how much CO2 you have. Get them to test your KH, they should be able to. Once you know your KH and pH you can use the chart to determine your CO2 content. I use Hagen test kits. They use color charts so you cant get it perfect, but I can get pretty close. They are pretty cheap too.


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## bms

*Ph rising rather than lowering...*

I do not have the test kit for KH yet, but my Ph is rising!! I measured it this morning (which supposedly since there is no light at night should be the lowest number of the day) at 7.2 (using color charts, aquarium farmaceuticals kit) what is happening!?


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## Sir_BlackhOle

Do you run your co2 at night? If not then your ph could rise overnight.


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## bms

I left it running all night.


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## aquoi

I don't use bubble rates to set my CO2 to nice levels.
I maintain my KH at 4 and then increase CO2 steadily until I get a pH of 6.7 to get 24ppm of CO2.

You can maintain a good stable KH with additional calcareous filter media (coral chips, limestone, etc) or by adding CaCO3 every water change.

CO2 and lights are 10hours a day. At night I aerate the water for 14hours to provide O2 for the increased demand. Something I learned from some ADA publication.


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## gpodio

If you do decide to airate your tank overnight, make sure you test your PH first thing in the morning prior to the turning off the air pump. In many tanks, plant uptake contributes to a small percentage of overall CO2 loss/consumption. Gas exchange actually accounts for most of the CO2 loss in a tank. Therefore, not everyone needs to aerate at night, actually for many, this would cause a bigger PH swing than leaving the CO2 running all the time.

Hope that helps
Giancarlo Podio


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## aquoi

My pH does swing but it doesn't affect my plant and fish health.


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## bms

My tank woke up to a 6.7-6.8 ph at 7:00 this morning, right before turning on the lights.

Good thing you touched on the Ph swing subject as that was going to be my next question.

I have read a lot that fish do not like Ph swings, but how much is too much... unless you have aPh controller (and maybe even then) there will be Ph swings... photosintesis ocurrs at daytime only, hence my CO2 concentration is bound to be higher at night...

What is the general concensus on leaving CO2 on at night or not? Other than CO2 how can one reduce Ph swings to a minimmum or at least to a level when it will not affect fish?


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## PeterGwee

The pH swing is of no issue...it occurs in nature as well and more rapidly then what we experience in our tanks. The issue here is whether there is a need to aerate in the first place? When plants are growing well, they saturate the entire water column with loads of O2 far more than any number of airpumps or powerheads can get in. Unless you are seeing fish discomfort in the morning due to lack of O2 (too much critters), you are just wasting away the O2 buildup by plants.


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## gpodio

I've never required air pumps for O2 levels and feel surface agitation is enough for most setups. The reason why some use pumps during the night is to avoid CO2 levels from becoming too high and possibly becoming dangerous. Although PH in nature will vary from rainfalls and changes in seasons, we are comparing it to a daily change from day to night, this may not be as "healthy" as nature's way of doing things. If your PH changes more than 0.4 between day and night, you could do a little better. If your fish don't seem bothered by your current setup, then don't change anything, they are probably used to it by now.

Due to the high CO2 levels I keep and low surface agitation, I have my CO2 powered diffuser connected to the light timer, this has proven to be the most stable in this tank, if it had more surface agitation I'd probably leave it on 24/7 but wouldn't be able to bring CO2 levels as high as I do now during the day.

It's all about balancing CO2 loss and diffusion rate, plant uptake plays a small part for tanks with moderate surface agitation/gas exchange levels.

Hope that helps
Giancarlo Podio


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## bms

OK, just got my KH kit...

I am measuring P = 6.8, Kh = 8 -> CO2=38.

I was told to shoot for CO2 between 20 and 30, so I know this level mey be a bit high...

When you talk about dangerous CO2 levels... what range are you talking about? Is CO2 dangerous to plant, fish or both, at what levels?


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## Sir_BlackhOle

CO2 can be dangerous to fish at extremely high levels. 38ppm should be fine, although a little high I believe. Try this site for great CO2 info:
http://members.cox.net/tulsaalstons/AquaticPlants.htm#High Pressure CO2


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## dennis

I have had co2 levels *much* higher than that and never had a problem. At time when I was fiddling wihtt he CO2 setup, or for other reasons, and the fish never seemed to mind. I at one point had had 11 neons, 2 golden barbs, and 2 otos in a 10 gal wiht tons of plants. I accidently hit 90ppm of co2 a couple of times. I know this lasted for several hours and the fish were not gasping or even acting funny. I do not recomend trying this and mine was an accident dut I generally have it int he 35ppm range adn no one cares. I only have 7 neons in there now, not because of deaths though My plants seem fine adn this is an easy number to stay at based on my water and co2 setup. I believe that part of hte reason mine can get so high wihtout any ill effects is the fact that my plants (and I have a lot) producea lot of o2 during the day. I am sure that even witht e high co2 levels that there is planty of o2 in the water, even after all night. For instance this morning I had 60ppm of co2 because I just changed my mix and it was not fine tuned yet. My fish are fine but my plants also produce fairly steady streams of o2 through out the day. One thing to remember is that co2 saturation in the water does not force out o2. At he end of the day, if your plants are growing well, your water will be highly saturated with both CO2 and O2.

ANyway, I ramble so hope this helps.


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## LordSul

Does it matter, from how deep the bubbles leaves the tank? For better diffusion is this important?

And, if I make a diffuser, so the CO2 stays in the water longer, does diffusers deepness makes any diffrence in efficiancy?


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## John N.

Hasan, the placement of your diffuser near the bottom of the tank is best.

You want the CO2 bubbles to be in contact with the water as long as possible. The bubble will dissolve into the water as it floats up. Placing the diffuser at the bottom will keep the CO2 bubble in contact with the water longer for maximum CO2 dissolution.

-John N.


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## LordSul

Thanks for the fast reply,

I have made my own diffuser from an old music cassete case. Im using the part that looks like a U shape. When turned upside down, the CO2 fills in it. CO2 being stable in the diffuser, does it still diffuse at maximum?


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## John N.

Sounds like you have a CO2 bell contraption.

If the big bubble is staying inside the cassette area, and not releasing any gas to the surface, Then you have a great diffusion method, and the rate it diffuses at is the same as the output. You are getting good co2 diffusion.

Test your pH and KH to see how much CO2 diffusion you are actually getting in ppms, compare it to the charts in the Fert section. You'll be looking for a drop in pH when adding CO2 compared to straight from the sink.

-John N.


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## LordSul

Well, it seems Im not getting any diffusion.. I had to turn off the CO2 supply off, (becuse of a technical problem but it will be back working tomorrow) I realised that the CO2 in my diffuser isnt decreasing, it seems that its staying in the water and not diffusing.

Also, my pH seems to rise...that is odd, my tap water is 6.8 whereas my tank water which is from the tap, yesterday was 7.2, today 7.3. This rise may be of the CO2 supply turned off.


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## Chris S

Is there a decent amount of current passing straight by that bell you made? You could benefit from flowing water directly past the CO2 bubble.


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## LordSul

The CO2-water surface in the bell seems very stable. 
So ,are you suggesting that, if I have the bell near the water surface where there is more water flow and current, CO2 will be diffused better?


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## Chris S

If the bell is directly in the current of the outflow of a filter return, The dissolution should be increased no matter how high it is. The idea is to keep as much CO2 in the bell till it can desolve. Current flowing directly over and around the bell will increase efficiency. Also , limit your surface disturbance if possible to minimize CO2 loss through the tanks surface.


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## Skelley

Call me stupid....
How is it that the current of the outflow will not minimize the co2 but turbulent waters will?


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## Chris S

Surface disturbace will. like aeration. current over a pure CO2 bubble will draw more CO2 from the bubble. It is like the reverse of the drying process. You dry your hair a bit quicker with a blow dryer right? That is because of the air currentpassing quickly and drawing the evaporation from your wet hair.
(I am a simple person that example makes sense to me)
Here is another and probably more relative example.
Fish breath in water. The reason is to expel CO2 and Intake O2. It is necessary for the water to be moving over the gills for the fish to breath ,right? 
Let the water move over the CO2 bubble so that it can breath. And dissolve faster into the water of the aquarium. 
If the surface of the tank has alot of disturbace and rapid current. In the form of waves or whatever, the tank is breathing more with the air to the rest of the room. It loses more CO2 to the room if this happens.


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## Skelley

Great explaination...thanks!


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