DIY CO2 Reactor for a Planted Aquarium





Introduction: 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

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?)

Step 2: STEP ONE

You want to make a hole in your bottle cap that is just a wee bit smaller than your airline tubings overall diameter. I used a pair of scissors to carve a hole, simply for the fact that I was too lazy to get out the drill, find the appropriate bit, and put it away, just for one hole. If you have more gumption than I, by all means, go ahead and drill it.

Step 3: STEP TWO

Make a slanted cut in the end of your airline tubing. This will make it easier to get in the hole on the cap.


Pull your airline tubing about 1.5" through the cap. If you are having troubles, try pulling with a pair of pliers. If you are STILL having trouble, you can shave a bit from the hole with a pair of scissors, or use a larger drill bit. Your call.


Ok, this is the part where I messed up when I was taking the pictures. Bear with me.

About 6-10 inches away from the cap, cut the line in half, and plumb in your check valve.

MAKE SURE that the arrow is pointing AWAY from the bottle cap, otherwise you will have a ticking yeast bomb sitting under your aquarium.

The picture is of the finished project. Just pretend you don't see that part though ; )


Now, here is the messy part. You want to use your aquarium silicon to put a nice bead around the inside and the outside of the bottle cap, sealing your tube to the cap. To smooth out the bead if you messed up, you can dip your finger in rubbing alcohol, and run it along the silicon. This will keep it from sticking to you too much.

You want to let this dry for 48 hours before using the setup.

Step 7: STEP SIX

Now, you want to make sure that your cap still fits. I got silicon on the threads of my first bottle cap, and it really messed with it, and I couldn't use it.

I don't think I need to explain how to put on a bottle cap. I'll give you guys some credit.


Now, plug your air diffuser into the other end of the line. It should fit fairly snuggly, and thats what we want.


Now, you want to add you suction cup to the end of the line with the air diffuser. Depending on your suction cup, the last step may or may not come before this one. I had to cut the side of my suction cup to get the airline to fit, so it came after in my situation.

Step 10: STEP NINE

Now you are ready to place the air diffuser in your aquarium. the ideal placement is low in the aquarium, and next to a filter intake, so the CO2 will diffuse more efficiently.

Step 11: STEP TEN

Ok, now its time to mix up your "CO2 juice".

I don't have any pictures of this, but its just like following a recipe.

First, you fill your bottle half way up with pretty warm water. You don't want it too hot, but not too cool.

Now you want to add 1of cup sugar.

You will need an extra cap that fits the bottle. You want to shake the hell out of it until you can dissolve as much sugar into the bottle that you can.

Fill the bottle up to about 2 inches away from the top with COLD water. Put on the other cap, and shake it some more. You want the water to be a little warm. Too hot, and it will kill your culture.

Now add teaspoon of bakers yeast, and just a pinch of baking soda. Give it a gentle shake.

Take your contraption to your tank, and screw on the cap with the hose, and let it sit. It might take up to 3 days to start bubbling, but soon, the yeast will metabolize the sugar, and produce CO2. The more sugar you add, the longer it will produce CO2. The more yeast you add, the faster CO2 will be produced, but it will deplete pretty fast. The baking soda is to keep it steady.

Every three days, give the bottle a gentle slosh around to mix it a bit.


Have a beautiful planted tank.

At night, when your lights are off, run an airstone to prevent pH swings.

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Sorry for asking too much a beginner question. is air stone and air diffuser the same..

Do you need some kind of valve to close co2 during nightime when plants are resting and not photosynthesising. I'm worried about overdosing on co2 which might be bad for fish.

Or u could buy a can of coopers and make booze u might actually want to drink ...

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

1 reply

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

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?

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

or u can use soap solution for smoothing out silicon 

Could you go into more detail about why the baking soda is needed? How does it "keep it steady"?

2 replies

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

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.

3 replies

. Maybe you would get more out of constructive criticism if you weren't so sensitive. ;) There is a BIG difference between silicon and silicone.

Minor details such as that don't really matter in the long run. You got the point I tried to get across, no?

Awesome instructable! For the air diffuser, might a standard aquarium air-stone work?

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! ;)

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!