How to Make a Planted Aquarium CO2 Generator/Infuser

For this Instructable, the first I've done in a while, I will be showing you how to use an old liquor bottle to create a stylish, nearly free, CO2 gas generator for a planted aquarium.  The aquarium I'm doing this on is a small Fluval Spec V, this will work for larger aquariums however, just up the bottle size and CO2 ingredients accordingly.  This should run about 2 weeks before needing to mix up another batch of the CO2 creating ingredients.

What you need:

1. 1 750ml bottle, emptied and completely rinsed out with fresh water (no soap, even trace amounts of soap can kill fish and may impede the CO2 production)
2. Enough aquarium air hose to reach from the spot you want to place the bottle to the intake on your aquariums filter or outlet of the powerhead
3. If the lid for your bottle is not already cork like or similarly air tight, a wine bottle cork... usually the same diameter of most liquor bottles will work fine.
4. A backflow preventer, commonly referred to as a check valve, that is the correct diameter for aquarium air hose.  Available for a dollar or two at most aquarium stores near where they sell air pumps and hose.
5. Super glue
6. Sugar
7. Baking Soda
8. Bread yeast

Suggested but not required for this build, especially if you intend to keep fish with your planted tank, is a CO2 test kit.  These are cheap, you can pick one up at your local fish store, or you can pick one up on Amazon for 15 bucks.  http://amzn.com/B0052M9886  If your CO2 levels rise outside of safe levels, just cut back on the CO2 ingredients detailed in this instructable, use a control valve, or consider only running it during the day by installing a common air hose regulator available for a few cents at the fish store and cutting it off in the evening, or pull the hose from the bottle if you're around enough to manage that.  Plants consume CO2 and put off oxygen during the day offsetting the CO2 being put out, but at night they consume Oxygen... and the combined effect could kill off your fish during the night.  There is a lot of literature on the internet about these concepts, and of course a lot of opinions... and a basic understanding of the ecology of a planted aquarium should be obtained before introducing anything new that may kill your critters off.

With this setup I haven't had any issues in this size tank, but it's always important to test water conditions with any aquarium on a regular basis.

In this aquarium, as an FYI, I have the following low light plants and critters:
Plants in Fluval Shrimp Substrate:
Java moss
Anubias
Moss ball
Java fern
Dwarf sword grass
Critters:
2 Porkchop rasboras
3 Blue rasboras
Zebra nerite snails
Ghost Shrimp

The rasboras will eventually outgrow this tank and the bio load will be too great, but I have other tanks to safely transfer them to when the time comes.

Step 1: Creating the Lid/valve

Pick your poison.  I chose a 750ml Old No.7 bottle, because I'm just classy like that.  The lid that came on this bottle was a regular screw top, which just won't do unless you want to play with expoxy and caulk to create an air tight seal, and likely make something pretty ugly.  A wine bottle cork would have worked just fine, but I found another bottle with a wine cork material insert with a black cap, even classier.

Take your chosen lid and the check valve to your drill press, a regular hand held drill will work fine too, just work out how you're going to hold the lid and drill through it safely, especially if you hastily consumed an entire bottle of your chosen poison to get going on this project.  Choose a drill bit that is slighty smaller in diameter than the point of largest diameter on your check valve, most of which are tapered somewhat.  The idea is to drill a hole you can shove the stem of the check valve into and get a tight seal in the cork like material.

Line up your lid/stopper so it's centered and drill all the way through.  In this case, since I chose a stopper with a black cap on top, I made one pass all the way through the stopper, then flipped it over and used a larger bit to widen out the top of the hole just deep enough to get through the plastic.  This was to allow my check valve to penetrate as deeply as possible into the cork like material (I say cork like because this one was that spongy plastic you often find nowadays in wine and liquor bottles, and is probably better for this purpose than cork anyhow). 

After you've made the hole to your liking, put a small amount of super glue onto the outside of the check valve's stem (make sure you know which way the air flows through your check valve, you want the air flow to go from the bottle to the aquarium, so glue and insert accordingly), and work it into the hole.  I wouldn't recommend putting glue in the hole first, you'll likely just block the hole and the airflow you'll need later.  Work the stem around a bit so there is glue in contact with the stopper around it's circumference, but not towards the tip where it could block the hole.

Step 2: Prep Your Filter

In order for this system to be really effective, you need to have a way of making big bubbles into tiny bubbles.  With some of the pricey off the shelf CO2 systems, that's essentially the part you're paying the big bucks for.  When this system pumps bubbles out of the airline, they come out pretty big... a lesson in surface tension.  One way of breaking those big bubbles down into smaller bubbles without introducing more equipment into the mix is to use your existing filter.

First, unplug your filter and remove it from your aquarium.  In the case of the Fluval Spec V, you just have to take off the powerhead output and the elbow joint on the hose and pull it out by the power cable.  If you're not using a Fluval Spec V, and you're using either a back hanging filter or canister filter... adapt.  The primary concept here is to get the bubbles to travel through the impeller fan that essentially any filter is going to have.  I did the same thing on another aquarium with a back hanging waterfall style filter, and in that case no drilling or dissassembly was required, I just ran the hose and wedged it into the end of the intake tube and it worked perfectly.

On the Fluval Spec V, the face plate for the filter comes off very easily.  Pop this off and take it to your drill.  Pick a bit that is the same or slightly smaller diameter than the aquarium airhose.  Mark the faceplate with a dot centered directly over the little impeller fan inside the unit, so that when the bubbles come out they get sucked directly into the fan, get chopped up into micro bubbles and spat out into the tank.  Drill your hole on the marked spot.

Once your hole is drilled, your airhose should slip into it and stay put, use a little super glue if you need to.  Do NOT situate the hose so deep that it interferes with the fan or the water flow into it... just barely breach the little faceplate.  Snap the faceplate back on and use a tiny zip tie to secure the airline hose to the outlet port on the filter body, without restricting that hose in any way or crimping or pinching off your airline hose.  Put your filter back into the aquarium, and hook the elbow joint and outflow valve back up the way you found it.  Run your airline hose to the spot you're going to stick your CO2 bottle.

Note to Instructables Contest Judges: I am adept at AutoCAD and Google Sketchup, and if I had a 3d printer I would make a new faceplate for this build specifically adpated to the purpose, and I would have a huge smile on my face, and I love you.

Step 3: Make a Batch of CO2

Now your hardware should be ready to go, and you're ready to whip up a batch of CO2 producing goodness.  First, in a small bowl or measuring cup, put a cup or two of fairly warm, but not hot water.  If it's too cold, tap cold, you won't get a good effect, or if it's too hot... you'll just kill off your yeast.  Just kinda warm by any standard is going to be fine.  Throw in about a couple teaspoons of sugar and mix with a fork until dissolved, the amount doesn't have to be precise but don't overdo it.  With the fork, mix in a marginally heaping 1/4 teaspoon of yeast, working the tines quicly at the surface to create bubbles and oxygenate the water.  This part is critical, you want to activate and oxygenate the yeast before adding it to your solution or your yeast will simply die off.  You want to let this sit for about 15 mins, working it with the fork every few minutes making sure to curn up any bottom setting yeast and working in that O2.

While that is sitting fill up your empty and well rinsed bottle about 3/4 of the way with warm water.  Using a funnel add 1 cup of sugar, really any sugar will do but the white stuff is the cheapest, and we're feeding yeast here.  Add 1/2 teaspoon of baking soda (this keeps the pH high, good for the yeast).  Using another undrilled cork, or if your thumb is big enough, plug up the end of the bottle and shake until all the sugar and baking soda is dissolved and not settling on the bottom.

Once approximately 15 minutes have passed since you added the yeast to your sugar water mixture, poor that mixture into your bottle with the sugar/water/baking soda mixture.  There is no need to shake or mix this, and that may in fact harm the yeast, just pour it in.

Step 4: The Hook Up

Now just cap off the bottle with the valve lid you made in Step 1, attach the airline hose from your aquarium, and wait.  If all went well it should have enough pressure and start producing bubbles after a few hours.   In the Fluval particularly, the bubbles generated are incredibly tiny, which is great for ensuring as much CO2 as possible gets dissolved into the water.  You will have to look very closely, and you will see an intermittent burst of tiny bubbles coming from your powerhead.  In the close up picture of the powerhead I have included here you can see how tiny the little bubbles are.  If you have the room really quiet and put your ear up next to where the filter pump sits, you can also hear what sounds like a tiny little fart as the bubble hits the impeller fan.

Step 5: Troubleshooting

If it goes overnight and still isn't producing bubbles something went wrong.  Either you have an a leak in the system somewhere, your yeast is bad, or the yeast wasn't properly oxygenated and prepared in the previous step.  As an example when I first set this one up, I wasn't getting bubbles... then I pulled back the lid and noticed that a bubble was rising, but in the filter chamber... in the course of putting the filter back in the aquarium my air hose had popped out of the pump vent, hence the zip tie I added to these instructions.  It could still probably pop out if inserted too hastily, so that's a good place to start looking for problems.  Another option would be to submerse the whole thing (minus the aquarium of course) in a bucket and see if you're getting bubbles anywhere you shouldn't be.  You can also check for bad yeast, mix up another couple cups of water and a couple teaspoons of sugar, and mix in some yeast.  It should get pretty foamy after an hour or so, if not, bad yeast.

If you have fish in your planted tank, they will probably be fine, but in some cases CO2 absorbtion in the water can get high enough to essentially suffocate your fish.  As any aquarium geek will tell you, watching your fish and learning how they behave is a critical part of taking care of fish.  This is no different.  As the CO2 levels rise, you will have plenty of time over days to notice the behavior of your fish change if the CO2 absorbtion is getting too high and your plants can't keep up, and the gas isn't aspirated fast enough into the atmosphere.  If your fish start hanging out at the surface more than usual, gulping for air at the top, or hanging out next to the powerhead or inflow and they weren't previously, you might be in danger of suffocating them with CO2.  If that's the case, you don't need to get rid of your CO2 system, you need to get more oxygen into the water.  Usually something that breaks up the surface tension of the water will suffice, like pointing your powerhead so it lightly breaks the surface tension of the water... or adding an airstone will do the trick.