Picture of DIY CO2 Reactor for a Planted Aquarium
This instructable will show you how to make your very own cheap and effective CO2 Reactor for a healthy, green planted aquarium.

Step 1: Materials

Picture of Materials
You will need:

A one liter gatorade bottle (or similar)
Several feet of airline tubing (vinyl is ok, but silicon is better)
An air diffuser
A suction cup to fit your tubing
A check valve
Aquarium grade silicon
A planted tank (duh?)
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unjust7 years ago
a note on brewing-- you cold also use simple things such as grape juice, or apple juice and brewing yeasts to produce your own wine instead of a mildly alcoholic water, or get fancy and use a home brew kit which is still remarkably easy. yeast don't produce high pressure co2, so you want your diffuser in as shallow water as possible, i'd suggest in the pump if you use an external filter as the water flow will help with disolving more co2. you could improve the pressure problem by running an air pump line into the cap, so that you're pressurizing the inside of the bottle to typical air line pressure, however this may (will) introduce a lot more oxygen into the brew than the yeasts may be used to/happy with, depending on the yeast, and evaporate some of the water.
deth2all unjust7 years ago
i was thinking this could make booze while reading the instructable,
Or u could buy a can of coopers and make booze u might actually want to drink ...
unjust deth2all7 years ago
you -are- making booze with this instructible
deth2all unjust7 years ago
so i guess the real question would be when to change the bottle as to not spoil the precious precious booze
unjust deth2all7 years ago
it would depend on what you're brewing. to use this as a co2 harvesting from brewing byproduct, i'd say disconnect it when it stops bubbling, and then let it age or continue slow fermentation as appropriate for what you're using.
I don't think there is a problem with the co2 pressure. The brewing process always has to work against the atmospheric air pressure of about 1.0 bar. If the diffuser is 50 cm below the surface, this will increase the total pressure to 1.05 bar. This means that the pressure will only be increased by 5%. This small change will probably not make any noticeable difference.
not quite. the brewing vessel and it's contents (if they're not rigid, as yours are not) are at equilibrium with the atmosphere (why you'll occasionally see bubbles back into a brewing vessel when there's a big weather change) as is the surface of the water. you're effectively adding a 50cm column of water for your co2 to overcome. while it will do this, it's adding 50cm of pressure to the container. not a lot, but it means that in order to get finer bubbles which will get more gas into the water, you need to overcome even more pressure to get it out of the fine aristone/wood. with a small enough hose this is reduced, however then you're looking at some capillary action. as a side note, how much co2 is a cup of sugar yeilding? as i recall glucose is 1:1:1 to co2 and ethanol, with table sugar a little less efficient. how much co2 does this translate into dissolved in the water vs lost to the surface, and how much do the plants need to make a difference? it's a really neat idea, i'm just not certain that it's terribly practical or significantly effective. (of course if you're using waste co2 from brewing it's somewhat practical.)
Sgt.Waffles (author)  unjust7 years ago
You don't want to run an air pump while the lights are on. When the lights are on, plants use CO2. The extra oxygen with using an air pump would displace the CO2, making the setup pretty much worthless. At night, plants run off of O2. All of that extra CO2 builds up, and swings the pH drastically, so its wise to run an airstone only at night to keep the CO2 from building up. A lot of people plumb these lines into the inlet of cannister filters too.
so i did this and it seems to be producing just fine.. i placed my air stone about an inch under water in my 55gal aquarium. Will this be deep enough to work? i also dont see any bubbles coming from my tiny air stone. what is going wrong? i have everything completely sealed off (air tight) with a very thick bond of glue. Whn i shake the bottle it bubbles like crazy and thats the only time i see the air stone pumping co2 out. HELP please, my plants have been doing

place your airstone little close to water level... sometimes to due less pressure it does nt come when it go down

MarkS258 months ago

You may better control the output from these by putting the entire contraption in a tightly sealed (tall kitchen) plastic bag with an air pump. With the pump on, CO2 is delivered to the tank by the pump - pump off CO2 inflates the bag for use later. Also, 2 bottles, started and replaced about a week apart make for a more consistent supply.

Can i leave my outside filter on during the day with the CO2 system. & pull the tubing out of the tank at night to keep the fish safe? Would this work?
jules152 years ago
Can you please tell me what you're using for substrate? and lighting? do you use fertilizer? Sorry if you already answered these questions previously, but your tank looks BEAUTIFUL and i want mine to look like that. thanks in advance :D
ksprabu3 years ago
or u can use soap solution for smoothing out silicon 
piesforyou6 years ago
Could you go into more detail about why the baking soda is needed? How does it "keep it steady"?
one of the byproducts of sugar fermentation by yeast is alcohol.  with the diy co2 reactor sealed, there is no way the alcohol escapes so it remains inside the container.  the alcohol alters the water's chemistry by changing the pH which, at some point kills the yeast.  the more yeast you add, the faster co2 (and yes, alcohol too) is produced.  the baking soda is added to buffer the change in pH and make the mixture produce yeast longer. 

i used the ff. recipe myself (using a 2-liter softdrink bottle)
2 cups sugar
1.5 liters water
1 tsp baking soda
0.25 tsp yeast

prior to using baking soda, my mixture at best lasts for 10 days.  after i added the baking soda, the mixture lasts at least 3 weeks.  the only problem i have with diy co2 is that the co2 bubble rate cannot be controlled precisely.
You could add one of those little flow rate "taps" inline before the check valve, as long as it's never closed all the way (that could get messy) -- this is what I mean http://www.theaquariumcompany.com.au/pages/products/showphoto/2319/?x=125&y=115&
Mitten7 years ago
Silicon =/= Silicone!!!!

That is my BIGGEST pet peeve.

Silicon is the metalloid used in semiconductors.

Silicone is the caulking and breast implants.

And now you know!
Sgt.Waffles (author)  Mitten7 years ago
Maybe you would get more out of an instructable if you didn't fret about trivial things such as an "e" or lack thereof. But thanks for the heads up.
. Maybe you would get more out of constructive criticism if you weren't so sensitive. ;) There is a BIG difference between silicon and silicone.
such as a typo?
Sgt.Waffles (author)  NachoMahma7 years ago
Minor details such as that don't really matter in the long run. You got the point I tried to get across, no?
oitsthatguy4 years ago
Awesome instructable! For the air diffuser, might a standard aquarium air-stone work?
AmyLuthien4 years ago
Or you can just lick your finger when you're smoothing out silicon. That's what I learned from my old dad years and years ago! ;)
Tracx4 years ago
Hi there Sgt. Waffles,
Even a long time after your tutorial, I've found it on the web and found it very useful. I've managed to get all the required equipment including a fancy mounting-thingy for my Nano cube for less than 10 euro's.

The CO2 exits just below the filter, where it gets dissolved in the water really quick. At night, when the filter is off, the excess co2 bubbles up and escapes at the surface.

I've seen bizarre results:
I was looking for a way to better grow my plants as they were getting brown and ugly.
I found CO2 was the solution, thanks to your tutorial a cheap one too, and now have nearly 100% green (some brown left) plants, that are happily growing -- some even centimeters per day.

Big thanks!
There is a very dangerous practice of letting this reactor go all the time.It should only be run while the lights are on.Plants reverse their co2 intake at night and this can very well kill all your fish. I would only run this every 2 to 3 days.I plan on making one thanks for the ingenuity and time.
EdgarVanKat5 years ago
Could I use backing powder instead of backing soda or would that have a different outcome?
This is a late comment, but those two things are very different chemicals.
kjfan15 years ago
toddstivers5 years ago
ive tried this and it doesnt work i need help
ace0075 years ago
Just get the bit out and turn it with your hand :-) If it's still new it will give you a perfect hole for the tubing
rklee20205 years ago
hi there it sounds like it will work great & very inexpensive, just one question though. is there a better time to have it runnning, eg day time only or night time only or can u leave it on 24 hrs. when i first started using this, my fish at night would all be at the surface acting like they where gasping for oxygen. so i turn it off during the night & only turn it on for a few hours during the day. & another question when do plants take in the most c02, daytime or night time? so i will be able to turn it on when its the most beneficial for my plants.
the ideal scenario would be a co2 reactor that runs only when there is light as that is the only time plants photosynthesize and give off oxygen as a by-product.
at night when there are no lights, plants use oxygen and give off carbon dioxide.
this can only be accomplished with pressurized co2 setups that use solenoid valves and a timer switch.

for diy co2 reactors, they are usually left running 24/7.  to avoid too much co2 buildup (e.g. at night), just make sure there is water movement at the water's surface.  when the lights are on, keep surface water movement at minimum when you have a planted tank.
acosicris5 years ago
good instructable..

i have a question, in step 4 what do u call that part of airline with arrow? Or should i ask.. where can i get similar of that? (in medical dextrose?)

Shaybah5 years ago
Super Idea! Leave the lights on 7/24, but try to position the the lighting so it doesn't shine on the front glass. The green stuff on the glass is not pretty. Another idea, you can use real fruit juice, and cut back on the sugar. I didn't see anyone asking what to do with the Solution left in the bottle after the bubbles stop. I'm just a country boy. Best Regards
do you need the check valve.
smegman6 years ago
Is that dwarf sag? yours is beautiful. can you give me any advice on lighting and substrate?
KDSinLA4446 years ago
I built a CO2 reactor very much like this one about a year ago, hooked it up to my (very small, 2.5 gal) tank, watched the little bubbles form abd float around, went to bed, and in the morning three of my fish were dead. I immediately disconnected it. And then started to wonder what was going on... ...Obviously, as this biological CO2 reaction is going on, carbon dioxide is being produced... But is not the only thing being produced! I understand that such reactors seem to work quite well for other aquarist, but when I took a whiff of just what WAS being pumped into my aquarium what I smelled was ALCOHOL! Now, of course, the brew is supposed to produce alcohol... But alcohol is also extremely toxic, and I can't imagine that some of it wasn't evaporating out of my CO2 reactor and then getting pumped into my little tank along with the desirable CO2. I have read several articles about these home-made CO2 reactors but I have never seen anyone address the issue of the possible absorption of the highly-volatile alchol into aquarium water. And I don't understand why... I mean, the stuff stinks! Who wants to pump "stinky" gas into their aquarium??? Also: couldn't I just hook up a bottle of carbonated water to my tank once a week or so and let the released CO2 from that provide me with all the carbon dioxide I need? And wouldn't this be safer than risking alcohol poisoning my fish? I am currently considering trying to used compressed CO2 from a local paint gun store, but I do not have the money to spend on regulators and bubble counters. I need a cheap, effective, and NON TOXIC method to aid my plant growth in a planted and fish-occupied MINI tank-- and I really don't want any more dead fish... Ideas??? Thanks!
Clearly, your Co2 setup produced way too much CO2 for your tiny tank. These setups are generally sized for 10g-20g tanks. You could try doing a little more research to find out if there is a formula for sizing to your tiny tank. Also keep in mind that plants produce CO2 in the absence of light. I.e. at night.
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