Easy and Cheap CO2 for your tanks
CO2 is incredibly intimidating, even for experienced planted tank nerds. In fact, I’m in a constant battle of wanting to inject CO2 into my tanks to grow plants better, and not wanting to drop $300+ per tank just on a CO2 system. After a lot of experience (and money spent), I decided to write this guide to help others CO2 inject their tanks for a bargain.
What you need
A CO2 setup needs a few crucial elements. First, obviously, is a source of CO2. In most cases, a regulator is needed to attach to that CO2 source and regulate how much gas actually leaves the source and gets into your tank. To make sure you know how much gas that is, you’ll also need a bubble counter, which is a little clear container full of water so you can see the CO2 bubbles travel through. You’ll also most likely need a solenoid, which is used to turn the CO2 on or off. Plants don’t really absorb CO2 without light, so you want to cut your CO2 off at night to prevent from gassing your fish and wasting your money. Next, you’ll need some way to get the CO2 into the water- most likely a diffuser. Diffusers create tiny little bubbles to mix the CO2 into the water. And finally, you’ll need a CO2 drop checker, which is a cheap little glass thing in your tank that turns different colors to tell you how much CO2 is dissolved.
You’ll also likely want CO2 tubing, which is extra-hard tubing (much more rigid than regular airline tubing) which helps prevent CO2 from leaking out at all. However, cheap airline tubing will still work.
Your shopping list:
Source of CO2
Regulator
Bubble Counter
Solenoid (And a timer or smart plug)
Diffuser or Reactor
Drop Checker
CO2 Tubing
The most important element of CO2: Co2.
One of the hardest parts about getting CO2 into your tank is just that… Getting CO2. There are many ways to get it, and you’ll see in plenty of places that the “best option” is just to buy a giant 5lb tank of CO2 and get it refilled nearby, or use paintball canisters, and so on and so on. Two big limitations are SPACE and LOCATION. A big CO2 tank takes up loads of space and looks ugly, so unless you have a large tank with a nice stand to hide it you’ll have a big industrial canister sitting in your living room. And at least in my location (Close to the capital of VA), it is extraordinarily difficult to find anyone willing to refill large tanks or paintball tanks. So what are your options?
Generate your own CO2. One of the easiest options, BY FAR, is the Neo CO2 Kit. This cheap little kit ($35 at the time of writing) includes absolutely everything you need to CO2 inject a tank. Just remember, this isn’t “high tech” CO2. It most likely won’t be enough to fully reach CO2 levels required by high tech plants, but it will help your plants grow much faster and more vibrant. The kit includes a cool generator bottle that uses a sugar gel and yeast to eat it and poop out CO2. It also includes tubing and a small diffuser, and it generates so little CO2 that a solenoid isn’t needed, and you probably won’t even need a drop checker as the levels won’t really reach dangerous levels (and you can’t adjust it). But if you want CO2 in a small tank for cheap, this is it.
Prefilled Paintball Canisters. If you’re limited on space but want real, pressurized CO2, one of the easiest methods is to use prefilled paintball canisters. For your setup, you can get the Fluval Pressurized CO2 Kit (95g) with almost everything you need. I say “almost” because, realistically, the kit sorta sucks. But it’s still the best way to get set up with prefilled canisters. With this kit, the regulator is honestly pretty solid, the bubble counter works fine, but the tubing can cause leaks and the diffuser is pretty bad. The way to go here is to purchase the kit for $85 (at the time of writing), then hook it up to a better diffuser or reactor, and ideally use better tubing. You will also need a solenoid for this kit, which you can get for around $20 on amazon, like this one.
The trick with this setup is to not buy Fluval’s overpriced CO2 canisters. Fluval wants to charge you $52 for 3 canisters ($17 a canister)- instead buy these from Walmart, which fit the regulator and price in only at $15 for 2 canisters ($7.5 a canister). But in a pinch, Fluval’s canisters are almost always available at your local pet store. These canisters last about 1.5 weeks on my high tech 20 gallon tank, and about 2.5 weeks on my high tech 6 gallon.
Fluval Pressurized CO2 Kit (95g) - $85
Solenoid - $20
Better Diffuser - $15
CO2 Tubing (And suction cups) - $12
Total: $132 for the entire setup. $7 canister refills that last about 1-2 weeks.
Sodastream. This is probably the most cost effective method for CO2 outside of just buying a big tank and having it refilled every few months for $5. Sodastream canisters are available at almost every major grocery and retail store. They’re $30 a canister, but you can bring your old canister and swap it for a new filled one for $15. If my math isn’t wrong, they’re about 760g which means they hold roughly 8.5x what the prefilled paintball canisters above hold, but only cost 2x as much to refill. They also have the benefit of lasting much longer, obviously, and they’re still super thin so they can be wedged into a corner and out of sight easily.
Your sodastream CO2 setup will need all products to be purchased separately for it to work properly. Check out the products below for the cheapest system I personally use:
Regulator + Solenoid + Bubble Counter - $37
Adapter to connect regulator to a BLUE Sodastream Cylinder - $28 (Make sure to get Sodastream CGA)
CO2 Tubing (And suction cups) - $12
Two Sodastream BLUE CO2 Cylinders (Do not buy the pink ones) - $60
Total: $143 for the entire setup (including a backup canister). $15 canister refills that last about a month.
I recommend purchasing two cylinders, since you need one to trade in and you don’t want to interrupt your CO2 supply to your tank. You can also upgrade the diffuser to a “Bazooka” style diffuser which will product smaller bubbles and be more efficient.
This setup works by connecting the CO2Art adapter to the top of the Sodastream canister. It is important to note that this particular adapter has a 90 degree elbow, because most adapters are straight and thus your regulator will wind up being sideways and your bubble counter will be horizontal. The regulator will connect to the adapter and will receive CO2 from the canister. Once the solenoid is plugged in and the other side of the bubble counter is hooked up to a tube, that tube can be led directly into the tank and to the diffuser.
Overreacting
One commonly overlooked element of CO2 is diffusion. As mentioned above, there are very few methods that are technically 100% efficient, meaning 100% of your CO2 is dissolved into the water. There are a few downsides of this lack of efficiency: You’ll wind up with bubbles in your tank which makes your water look like Sprite, and you’ll be wasting CO2 as some small bubbles pop at the surface.
In my experience, no matter the diffuser you use, you’ll ALWAYS have some amount of bubbles in the tank or popping at the surface. Inline diffusers are worse, even the high end ones.
The solution? Reactors. They sound complicated, but they really aren’t. The basis of a reactor is simple: CO2 bubbles go up, water goes down. The strategy is to basically mix water and CO2 inside of a chamber, where water and CO2 enter through the top and only water can exit the bottom. Since CO2 bubbles will rise, you’ll never have any bubbles leaving the reactor, meaning all CO2 you add to your tank will ALWAYS be dissolved. Of course, it is worth noting that to use a reactor you either need to be using a canister filter or an external pump / sump setup.
The only real downside of using a reactor is flow rate. Since they’re big tubes full of water they naturally slow down the flow rate of your filter, so you’ll want to make sure your filter is considerably overrated for your aquarium size just to be safe (which it should be anyway!)
I write about reactors because I honestly love them- they’re a genius way to improve your efficiency and prevent the Sprite effect in your tank. They also mean no diffusers are visible in your tank so you can hide absolutely everything but your filter inlet and outlet. And if you really want to be fancy, you can even build a reactor with the heater built in so that isn’t in your tank either. And as a bonus, if built right they’re completely silent. No bubbles, no whining noise, nothing.
Buying a reactor.
There are lots of reactors you can buy, most are extremely expensive. One of the best ones available is NilocG’s Cerges style reactor, which is around $85. Personally, I don’t find that worth the money. You can also pick up a considerably cheaper one from the brand ISTA, such as the ISTA Turbo reactor for $35 on Amazon or even the ISTA MaxMix for as low as $20. I’ve personally used the MaxMix which, frankly, sucked. It was loud and leaked all over the place, and even after heavily modifying it the only way I could keep the damn thing from leaking was to superglue the entire thing together so I could never open it up again.
Building a reactor.
You can find loads of guides online, the two most popular reactor types are Cerges and Rex Griggs reactors, with the only major difference being how water leaves the tube (Cerges has a straw at the bottom which leads out the top, Rex Griggs just lets water out the bottom). I personally built my reactor Rex Griggs style, which wound up being fairly simple and costing me around $30. There are plenty of guides available, but I’m happy to provide instruction to anyone who asks. Simply put, the reactor is about a foot long, 2” ID pipe with a cap at either end (one cap is unscrewable for maintenance). I got a plastic barb fitting the size of my filter tubing, and a small brass barb fitting the size of my airline tubing. Then I used a step drillbit to drill an inlet hole for the water at the top of the tubing, a smaller inlet hole at the very top cap for CO2, and an outlet hole at the bottom. And I adhered my barb fittings into those holes with a little aquarium silicone. I finally filled it with a few bioballs to break up the bubbles, and it works perfectly!
Hopefully this helps someone. I wrote way too much hoping me spending way too much will help someone else. Best of luck!
