How to Setup a Paintball CO2 System for Your Planted Aquarium

Putting together a paintball CO2 system for our aquarium was one of the best moves I have made for our tank.  I was always hesitant to install pressurized CO2 because of the cost and complexity.  It can be intimidating getting all the parts installed as there is not much in the way of instructions currently on the web.  I hope this page offers some guidance and confidence in transitioning to pressurized CO2.  To understand why CO2 systems are beneficial to planted aquariums, check out my page on planted aquarium basics.

CO2 System Primer – Goals for a Nano System:

Paintball CO2 systems are a good match for nano and small aquariums.  If you have a tank of 20 gallons (75 liters) or larger, you probably want to think about utilizing tanks larger than paintball.  However, less than 20 gallons is a good match for Paintball tank systems.

Paintball CO2 system on a Fluval Spec V Aquarium

First, let me explain the various sizes of pressurized CO2 tanks.  CO2 tanks contain carbon dioxide under enough pressure to be in liquid state.  The tanks are categorized by the weight of liquid CO2 they can contain. The smallest systems are based on disposable cartridges and they typically contain from 16 grams to 88 grams of CO2.  Next up are paintball tanks, which are commonly sold in 20 or 24 oz.  Lastly are the larger industrial type tanks that start at 2.5 lbs and go up to 40 lbs.

In choosing the tank size for our 5 gallon Spec V, I wanted a tank size that was large enough to go several months without refilling and at the same time, match the scale of our small aquarium.  The 20 oz. paintball tank fit the bill perfectly.

Beyond the size of the tank, other criterion I deemed important:

  • Reasonable Budget:  I wanted to assemble a system that is a good balance of price and reliability.
  • Consistency: I understand many people experience frustration with systems that do not operate the same day in and day out.  I wanted consistency in the CO2 output.
  • Simplicity: I don’t feel having more adjustments is always better, and I wanted a regulator and system with minimal knobs to adjust.
  • On/Off Capability: In order to best control CO2 distribution and save gas, I wanted the ability to put the CO2 regulator on a timer to control when CO2 is injected into the tank.

Components for an Aquarium Paintball CO2 system

I’m going to present to you what components I recommend to assemble your own paintball CO2 system. After I go over the components, I will discuss where you can get these parts, and I will give you some tips on how to get it all assembled and running. Here we go. . .

Components and Accessories:

Regulator and Needle Valve:

The regulator is the heart of any CO2 system.  It simply knocks down the pressure from what is in the tank (around 62 Bar / 900 psi) to a lower pressure that can be used.  Based on my constraints of small size and reasonable cost, I decided on a simple single-stage regulator.  There are several brands that are similar – here are some characteristics of this family of regulators:

  • Single Stage: as opposed to dual stage.  For a small setup, you can still get very good control with a single stage regulator, and it saves you big bucks.  Single stage regulators used to give up precision and reliability (compared to dual stage regulators), but that is not necessarily the case anymore.
  • Non-Adjustable Pressure Output: For simplicity and cost savings, they have a set (non-adjustable) output pressure of (3.5 bar / 50 psi).
  • Single Gauge: that displays the pressure in the tank.  This always stays the same pressure of around 62 Bar (900 psi) until the tank starts to run empty, at which point the pressure starts to drop.
  • High Precision Needle Valve: The regulator either comes with a high quality needle valve installed, or comes with one that you install downstream of another (coarse adjustment) valve.  This is what you use to control the rate of CO2 flow to your tank.
  • Solenoid Valve:  You can get a regulator that stays on all the time, but I’d recommend getting one with a solenoid valve.  Put it on a timer – when the power is on, the valve is open and CO2 flows; when the power is off, the valve is closed.
  • Threading Connection: The budget regulators of this category generally come with threading common for the UK, Europe, Taiwan known by various nomenclatures: BS341 / DIN477 / W21.8.  This is different than the typical threading of large tanks in the USA (CGA 320).  However, this is no problem as we are mating this to a paintball tank, which will require an adapter.  I will get into this more next.
  • UK or European Origin: For whatever reason, regulators with all the characteristics presented are not readily available in the USA.  This may change in the future.

Here are a few good options for regulators to consider:

Single Stage with Single Gauge: This is the regulator that I purchased and is shown throughout this page. It is available from both CO2SuperMarket and CO2Art although they are both out of stock at the moment. Make sure to click on options to include the fine adjustment (pico) valve and get the correct voltage / plug for your country.

single stage, single gauge CO2 regulator

Single Stage with Dual Gauge and Adjustable Outlet Pressure: This is newly available from CO2Supermarket. It has dual gauges that show tank pressure and also outlet pressure. It is slightly more expensive than models with set outlet pressure, and it is bulkier. It is relatively cost effective considering the features and that it comes standard with the high precision needle valve.

Intense CO2 Regulator V3: This one is a real beauty. Too bad I can’t find it in stock anywhere.


Paintball CO2 tanks are readily available in 12oz, 20oz, and 24oz capacities.  I decided to go with a 20oz tank because, being slightly shorter than the 24oz variety, I thought it would fit better under our kitchen cabinet uppers.  All the tanks are very similar in pricing.

20oz paintball tank

The tanks come empty; I will talk more later about getting it filled with CO2.


As I alluded to above, we need an adapter to enable us to mount the regulator (with UK threading) onto a paintball tank.  Paintball tank threading is the same in the UK, USA, Europe, etc.

Paintball to BS341 regulator for CO2 system

The adapter is simple enough – female threads that attached to the CO2 tank, male threads for the regulator to attached to, and an adjustable assembly that presses the pin on the paintball tank to enable gas to flow.


CO2 systems are under under considerable pressure, even after the regulator.  Delivery pressure is around 3.5 bar (50 psi).  You want to use tubing and fittings that are appropriate for CO2 and at this pressure.

Don’t use regular air hose that you get at the pet store.  It isn’t rated for this delivery pressure, it is permeable to CO2 (meaning it will leak some through the tubing material) and it will discolor and become brittle over time.

Get tubing made for CO2 delivery. Get more than you think you need as you might change your mind on how things are located and configured.  You can get CO2 tubing in black or clear based on your preference.

Bubble Counter:

Bubble counters are devices that you fill with water and place in the CO2 line between your regulator and aquarium.  CO2 flows in the bottom and the CO2 bubbles flow through the water to the top. Bubble counters allow you to see and measure what effect your needle valve adjustments are making by counting bubbles rising through the contained water every minute (or second).

Bubble counters are of two types: inline and regulator mount. As their name suggest, regulator mount bubble counters have a bottom fitting that allows you to attach directly to the outlet of your regulator.  Inline bubble counters have a hose fitting on either end.  You can place an inline bubble counter anywhere, provided it is oriented vertically.

inline bubble counter with integral check valve for aquarium CO2 system

I chose to get a bubble counter that also includes an integral check valve.  This means that the assembly will prevent water from siphoning back through the attached tubing to the regulator.  If you don’t get a bubble counter with a check valve built in, it is important that you install a check valve separately to prevent from this scenario.


There are two main categories of dispersing CO2 into your aquarium water column: Reactors and Diffusers (or Atomizers).  Reactors allow all of the CO2 to be absorbed into the water column before being dispersed into the tank. Diffusers, on the other hand, create very small bubbles of CO2 (very fine, almost like mist) that are dispersed into the water.  They are typically installed in the display tank. There are various opinions on which genre is better.  In the interest of space (reactors tend to be large) and simplicity, I suggest a diffuser to start out with.

Diffusers are further broken down into two types:  in-tank and in-line. I hope to try out an in-line diffuser in the future (which will be installed in the flow tube between the pump and outlet nozzle of our Spec V). However, I decided to start with the simplest solution; a bazooka brand atomizer.

CO2 atomizer bazooka diffuser

The Bazooka atomizer passes CO2 through a ceramic type material that produces the very fine CO2 mist. They are available in varying lengths; we only need a small one (like this, good for aquariums up to 120 Liters (32 gallons).

Drop Checker:

A drop checker gives you a visual indication when you are close to the recommended CO2 concentration of 30 ppm. They are very limited by being slow reacting and of limited accuracy; however, it is invaluable as a beginner with a brand new setup.

drop checker with premixed indicator solution

Get a set that includes the glass bulb, a suction cup (to affix to the inside of the aquarium) and, (most importantly) premixed drop checker solution.

Other Tools and Accessories:

There are a number of other small items you need to consider having on hand to get your system up and running:

  • Adjustable Wrenches:  You need two of these (medium sized) to tighten adapter onto regulator, and regulator onto paintball tank.  I now know these are called ‘spanners’ across the pond – cool!
  • Teflon Tape:  Otherwise known as ‘plumbers tape’, I suggest using this on every threaded metal to metal or metal to plastic connection in the system.
  • Nylon Washers: You need a nylon washer between the regulator/adapter and between the adapter/tank interfaces.  The nylon washer is what provides the seal and will enable a leak-free system.  Anytime you take apart one of these interfaces (like when you go refill your tank) you need to plan on replacing the associated washer to ensure it will remain leak-free.
  • Kitchen Shears:  Good for cutting the sturdy CO2 tubing.
  • Fittings: CO2 tubing is very stiff and difficult to route into tight bends.  I couldn’t get the tubing to cooperate and go where I wanted until I added some 90° elbows.  What I use are 6mm pneumatic fittings.

4mm / 6mm pneumatic 90 degree elbows used in CO2 system

  • Timer: You will want an outlet timer to control the solenoid valve.  I now use smart plugs for all of my aquarium automation for this purpose.

Vendors – Where to Purchase:

Normally, I suggest getting items through Amazon.  I monetize this website through amazon links so trust me, I use Amazon where I can.  However, it is very difficult getting good CO2 equipment through Amazon USA.  Amazon UK is a bit better, but it’s hard to get all the items you need in one place.

Paintball CO2 system components and accessories from CO2Supermarket

I have found a few direct retailers in the UK that I would recommend:

  • CO2SuperMarket: I purchased my equipment from them, everything I needed save the 90 degree elbows. Very reasonable prices, very convenient with everything I needed in one place. Free shipping to USA! The only downfall is slow shipping to USA, taking almost 3 weeks to arrive. You can piecemeal everything one part at a time, or they have kits available with everything you need. Brilliant.
  • CO2Art: Another UK vendor, similar to CO2SuperMarket.

eBay: The disadvantage is getting everything piecemeal will be a real pain, and customer service may be a problem depending on the vendor or individual you are working with.

Options and Systems I Don’t Recommended:

There is a seemingly good paintball system from Aquatek. It attaches to a paintball tank with no adapter, has dual gauges and allows for outlet pressure adjustments, and says it includes a fine adjust needle valve. I haven’t used this system, however, I have read carefully all the reviews on Amazon. It is apparent this unit will lead to much frustration as the needle valve sucks. Life is too short – don’t waste your time on this.

Also, I do not recommend any system that relies on disposable CO2 canisters (20 gram, 88 gram, etc). These systems are small, yes, but the operating cost of replacing these tiny canisters is criminal.

Putting it all Together:

I’d expect that most people’s final selection of equipment and regulators will vary from what I have installed. However, I’ll go ahead and present the steps for how I installed our system – much of which you should be able to apply to your setup.

Step 1 – Get Some Gas:

Purchased CO2 tanks are empty when delivered, so you need to get it filled.  As the name suggest, paintball canisters are intended for the sport of paintball.  You can get them filled at some sporting stores.  I don’t know specific places in the UK.  In the USA, I take our empty tanks to Dicks Sporting goods.  They fill our 20 oz tank for less than $6 USD.

Consider getting two tanks so that you can have a redundant one already filled and ready to swap in when your installed tank goes empty – no down time scurrying to get your only tank filled.

Step 2 – Ready the Regulator:

I ordered a regulator that came with a ‘pico’ needle valve to allow very fine adjustment of the flow rate.  What I didn’t know was that this valve shipped separated and is intended to be installed downstream (after) the needle valve that comes with the base regulator.

It is easy to install; just unscrew the hose connector that comes stock and replace with the pico valve.   Make sure to use teflon tape on the metal to metal threading.  Tip: when using teflon tape, wrap over the male threaded part in a clockwise direction.  Tighten with your adjustable wrench.

CO2 regulator with fine adjustment needle valve for nano Aquarium

The next item is to attach the adapter to your regulator.  First, make sure to place a nylon washer inside the regulator and another (appropriately sized) nylon washer inside the female side of the adapter (in preparation for connecting to the tank).

paintball adapter mounted on CO2 regulator

Put teflon tape on the male end of the adapter, then use your two spanner wrenches to tighten (in opposite directions).  Put moderate force on the wrenches to get it nice and tight.

tightening paintball adapter onto co2 regulator using adjustable wrenches or spanners

Next, you need to adjust the pin inside the adapter.  Gas is allowed to flow from paintball tanks when the pin inside the center of the tank nozzle is depressed. If you look in the female end of the adapter, you will see a screw that will depress the pin on the tank and let the gas flow from the tank.

pin inside paintball co2 adapter

The depth of this screw is adjustable with a flat head driver.  I screwed it fully in (away), then rotated a few turns to move it towards the paintball tank.

Step 3 – Attach the Regulator to the Tank:

One important thing to remember about connecting your CO2 tank to your regulator, and this applies to other regulator types as well: Do not install pressurized CO2 onto a closed regulator. The sudden surge of 900 psi pressure onto a closed regulator can damage the internals.  So, whenever you are attaching a tank to a regulator:

  1. Open the needle valve fully.  In my case, I need to open both valves as I have the main needle valve and the smaller pico valve.
  2. Plug in the solenoid.  When the solenoid is energized, it is open.

At that point, you are ready to install the tank onto the regulator / adapter assembly.  Apply teflon tape to the male threads of the tank.

installing teflon tape onto male threads of paintball CO2 tank

Check again that there is a teflon washer in the regulator adapter.  Now just use your ‘spanner’ wrench to tighten the regulator adapter onto the tank (held by your hand).

tightening co2 regulator onto paintball tank

As you tighten onto the tank, you may hear gas escaping out from the connection.  Keep turning until it is as tight as you can get it (within reason).  At that point you should see the gauge read around 900-1000 psi and hear gas gently flowing from the regulator.  Close the needle valve fully to stop the gas flow.  Unplug the solenoid.  Good job!

Two things can go awry when attaching the tank and they both involve the adjusting nut inside the adapter.  If you tighten the adapter fully tight onto the tank and no gas flows (gauge reads zero), you need to remove the adapter from the tank and adjust that pin further out (downwards, toward from the tank).  Conversely, if you fully tighten the adapter on the tank and there is large amounts of gas escaping and you can’t fully tighten onto the tank, remove and adjust that pin further in (upwards, away from the tank).

co2 regulator mounted onto paintball tank

Step 4 – Assemble Components from Regulator to Diffuser:

From here on out, it’s just an effort of getting all the pieces in place from the regulator to the diffuser. The CO2 tubing is connected to various devices using either pneumatic push-in fittings or a compression collar fitting. The push-in fittings (in my setup, used for connection to the regulator pico valve and at the 90 degree fittings) are exactly as they describe – simply push tubing into them in until it stops. To remove, you push the little plastic rim collar in toward the fitting and pull the tubing out.

For the compression collar fittings (used at the bubble counter and diffuser), first soften the end of the CO2 tubing you are attaching in warmed water.

using hot water to soften ends of co2 tubing for installation

Unscrew the collar to remove, then route the tubing through the removed collar. Next, press the CO2 tubing over the nipple on the device (careful – don’t break the nipple). Last, screw the collar back down over the tube/nipple.

inline bubble counter for aquarium co2 system

You can place the bubble counter anywhere you want between the regulator and the aquarium. It needs to be oriented vertically. To set it up, unscrew the top and fill 3/4 full of tap water.

inline bubble counter

This water will evaporate slowly over time and will need to be refilled every month or two. The bubble counter I purchased has suction cups to attach to glass. Unfortunately, the best place on my setup is at the end of our Spec V aquarium and the cups don’t stick to the frosted glass in that location. Oh well – I arranged the tubing and fittings so it hangs in place.

For our setup, I arranged the 90 degree fittings to get the tubing up and over the end of the Spec V, routing across the pump section. I am now running our Spec Topless so I don’t have to route around the acrylic top. I drop the hose straight down to the location of the diffuser. For those using the acrylic top, I would suggest looking into cutting a slot in the top to simplify CO2 hose routing.

bubble counter and diffuser mounted on spec v aquarium

Regarding placement of your diffuser in your tank, remember that the goal is for the small CO2 bubbles produced to be distributed throughout the aquarium. The best way for this to happen is to place it below the flow nozzle that distributes water through the tank. Place the diffuser as low as possible, but about 1-2 cm above the substrate level. As bubbles rise, they will start to dissolve before entering the flow stream from the pump nozzle.

bazooka co2 atomizer for nano aquarium

Step 5 – Install your Drop Checker:

Provided you purchase a drop checker that came with pre-mixed drop checker solution, setup is very easy. First attach the suction cup to the glass bulb. Next, rotate the whole thing upside down and start placing solution in a few drops at a time. You can rotate the whole bulb around to get the solution into the bulb and air out. Keep putting a few drops in at a time and check (by rotating) right side up until the bulb is about 1/2 to 2/3 full of solution.

nano drop checker

Attach the drop checker to the inside glass of your aquarium, open end pointed down. I suggest placing on the opposite end of your outlet nozzle, about 1/3 of the way from the top.

One word of warning, most drop checkers are glassware and need to be carefully handled to avoid breakage. I was possessed at some point to take the bulb off the suction cup and snapped the connection right off. I superglued it back together, but it was never the same (kept breaking).

Step 6 – Gas Flow Adjust and Timer Setup:

Now comes the fun part of getting gas in your tank! There is no easy way to describe all of this, so I will have to dedicate a separate page for dialing in your CO2 flowrate.

In short, start by getting your solenoid setup with a timer. Generally, you want the CO2 solenoid energized (flowing gas) in sync with your light timing, with one small adjustment. Have the CO2 solenoid turn on about an hour before the lights turn on and have the solenoid turn off about an hour before the lights turn off. This will let the CO2 levels be ramped up and ready to go when the lights turn on and, in an opposite manner, the CO2 will start to be consumed and lowered by the time the lights turn off.

paintball co2 system installed on nano aquarium

For the CO2 flowrate adjustment, start with the needle valve fully closed. In my case, with two valves in series, the main valve is fully open and the pico (fine adjustment) valve is fully closed. Apply power to the solenoid to open. Next, start opening the adjustment needle valve slowly – observe bubbles rising in the bubble counter. Make small adjustments until you get the flowrate you desire. Again, I will have a separate article with tips on getting the flowrate setup.


I hope you find this page helpful. Please let me know as products change in availability or features and I will try and update for everyone. Again, getting our CO2 system going has been immensely satisfying, allowing us to use exotic “high maintenance” plants, keep algae low and enjoy growth as fast as we dare. Best of luck to those who are planning on following in this adventure of the high tech planted aquarium.

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