Source: BeverageFactory CO2 Tanks
A regulator simply reduces the pressure of the gas from the bottle to usable amounts. There is not much to be said about regulators, you have hundreds of models to choose from. For the budget minded or pure DIY person a standard regulator such as this one will suffice:
Source: BeverageFactory CO2 Regulators
For those looking for the least amount of work and DIY tasks, a complete regulator may be more interesting. Those interested in using PH controllers or want to turn off CO2 at night, these are your best solution. These regulators come with needle valve, check valve, solenoid and bubble counter:
Source: JBJ Regulators on eBay
A needle valve allows minute adjustments to be made to the amount of CO2 going into the tank. Considering we are talking 30-60 bubbles per minute on an average tank, it's obvious that we need an accurate needle valve that will provide a stable rate. I have been very satisfied using needle valves from Clippard:
Source: Clippard part number MNV-4K2
Clippard 1/4" male to 10-32 female adapter, part number 4CQF-PKG (required to screw the needle valve onto the regulator)
Source: Clippard part number 4CQF-PKG (old SKU: 15006-3)
A check valve stops water from flowing backwards from the aquarium to the CO2 tank. Although this will not happen while the CO2 is being erogated, it can happen when the CO2 runs out or something is disconnected during maintenance. Seeing you don't want to flood the house or send water into the regulator, a check valve is a must in my opinion. You can use a regular plastic check valve used for air pumps, this should be changed at least once a year as the CO2 gas will damage it. Otherwise my personal choice is the Clippard MCV-1 brass check valve. If you're buying the needle valve above you shouldn't even think twice about adding this to your order, it's only a couple dollars more and far better than the plastic models.
Source: Clippard part number MCV-1
Source: Regular airline check valve
A bubble counter allows you to monitor the rate at which CO2 is being erogated into the tank. While it provides little to no hint as to the actual concentration in the tank itself (more on this later), it does allow you to adjust the needle valve quickly after maintenance or to make minor adjustments to the bubbles per minute that are dosed. A bubble counter, if not purchased with a complete regulator shown above can be added inline to any setup. Here's an example:
Source: Dennerle Bubble Counter
Alternatively, you can also choose not to use one. I use a valve manifold on all my CO2 tanks and one feed goes to a short tube I push under water to check the bubble rates when needed.
CO2 proof tubing
You'll need tubing to bring the CO2 into the tank. I use regular soft silicon airline tubing as shown below. Although not 100% CO2 proof, it holds up well over 2 years and is cheap enough to replace once a year:
Source: Soft silicon airline tubing
Source: CO2 proof tubing
A diffuser is something that diffuses the gas in the tank, similar to regular air stones... In short, the gas is pushed through a porus medium that releases it in the tank as a fine mist of CO2 bubbles, the finer the better. These bubbles are partially absorbed into the water molecules as they make their way up to the surface. Obviously any bubbles that do reach the surface are usually lost to the atmosphere and so it's safe to say that a diffuser is not as efficient as a reactor. A diffuser should be made of ceramic, glass or other CO2 proof material. Regular air stones are not going to work as the CO2 breaks the bond of the glue holding them together. On the low end there are the ceramic Micro Bubblers from Rena, otherwise a glass diffuser as shown below:
A reactor on the other hand usually consists of a chamber where water is pushed downwards through the chamber and CO2 bubbles are diffused from the bottom. As the bubbles try to float to the top, the water flowing down keeps them trapped in the reaction chamber until completely absorbed by the water. Little to no CO2 is wasted using this method however it is a more complex and expensive method of diffusion, of most interest to those with tanks around 55 gallons and bigger. Reactors can be placed inside the tank (an eye-sore) or externally in a closed loop or inline with a canister filter.
Source: CO2 Accessories
DIY: DIY External Reactor
DIY: Converted gravel vacum
If you have a canister filter you have one more option. That is to send the CO2 directly into the intake tube and use the canister filter itself as a reaction chamber. Initially I was a little hesitant in doing this however since I tried it I have not looked back since. I find this to be the best compromise between esthetics, simplicity and efficiency. It requires no added equipment, it's next to invisible and is just as effective as a reactor. You obviously want to make sure your canister expels trapped air/gas easily and will not "airlock". I use Eheim Classic series canisters in all my tanks and have never had one airlock due to CO2 or other trapped gasses in the canister.
Other interesting products exist such as combination units and complete CO2 startup kits.
Putting it all together
This is the simple part :-) Let's start off with placing the regulator on the bottle and assuring we have a good seal. The regulator should have come with a plastic washer that is used between the regulator and tank to make a good seal, no teflon tape should be used on this side of the regulator as the seal is made by the plastic washer and not the threads themselves.
To test the seal, close the regulator by turning the adjustment screw counter-clockwise until it turns freely. Open the tap on the tank, you should see the high pressure gauge indicate the pressure inside the tank. Now close the valve on the tank and wait about 5 minutes. If no leaks are present, the pressure inside the regulator should not drop even with the tap on the bottle turned off. If you encounter problems and can't get it to make a good seal, use a brush to "paint" some soapy water around the connections to find the location of the leak.
Next is the needle valve assembly for those that purchased a standard regulator. If you purchased a Clippard check valve you will want to place that between the needle valve and adapter.
Use teflon tape to screw the adapter into the regulator, be careful not to allow any pieces of tape to enter the regulator housing or possibly make their way to the needle valve. The rest of the Clippard fittings use an o-ring to make a good seal and can be hand tightened. We'll only be using pressures around 10psi so making a good seal on this side of the regulator is rather easy.
Connect the tubing to bring the CO2 into the tank and connect it to whatever method of diffusion you have chosen to use. If you are using a regular inline check valve make sure you connect it somewhere between the needle valve and diffuser/reactor. If you are also using an inline bubble counter, place the check valve between the bubble counter and the diffuser/reactor.
Setting the pressure
Close the regulator by turning the adjustment screw counter-clockwise until it turns freely. Open the needle valve a couple turns, this is to avoid damaging the valve in case too much pressure is sent to it by mistake. Open the tank valve. No CO2 should be coming out however the high pressure gauge should indicate the pressure inside the tank (Around 800psi when full). Close the needle valve (never overtighten) and slowly turn the regulator's adjustment screw clockwise until the low pressure gauge reads 10psi.
Open the needle valve to test the unit, some diffusers require a little time for pressure to build up and start diffusing. It's impossible to say how much CO2 is required for any given tank, best thing to do is to start low and monitor the CO2 concentration using the KH/PH Chart. A conservative starting point would be a bubble every 3-4 seconds. Aim for an initial CO2 concentration of around 15-20ppm, you can figure out exactly how much you want later based on your own tank.
Some useful information regarding measuring and controlling CO2 levels and avoiding PH crashes can be found towards the end of the DIY CO2 article.
The products I have chosen to show in this article are indicative of those I've successfully used in the past or products I know to be acceptable for the task. This article has been edited and reproduced by third parties to promote their own products and redirect links to their own store (Example). Please note that these versions were edited without my consent and may contain information, links and depict products which I cannot speak for or endorse.