CO2

WHAT IS IT AND WHY DO PLANTS NEED IT?

Carbon (in the form of carbon dioxide or CO2) is a basic building block for plants. Terrestrial plants can absorb loads of carbon dioxide from the air and through their roots because it is abundant in the atmosphere. However, CO2 is a scarce resource for submerged (underwater) plants. Naturally, small quantities of CO2 (around 5-8ppm) come from bacteria, fish respiration and natural gaseous exchanges in lakes and rivers. Plants grow upward towards the surface not only for greater light intensity but also to emerge themselves out of the water and take in CO2 from our atmosphere. In a planted aquarium I recommend injecting CO2 into the water, so it is no longer a limited resource, which really ramps up plant growth.

With all that being said, there are a couple of dangers of injecting CO2 in a planted tank. One is that you have a pressurized cylinder sitting around your house that could rupture if not cared for properly. Another is that too much CO2 can kill livestock in your tank if too much is injected; you may have heard the expression “gassing your fish”. But as long as you pay attention to your tank (especially when you first introduce CO2), have the right equipment, and don’t “jerry-rig” anything, it should be smooth sailing for you.

You may hear that an alternative exists in dosing liquid carbon…sounds easy, right? But let me be clear. Dosing “liquid carbon” does NOT provide an adequate source of CO2 to sustain plant life. In fact, it is not liquid carbon at all. It is glutaraldehyde, a disinfectant that breaks down into VERY small amounts of CO2. Not enough to be sustainable. However, it is great at killing black beard algae, or BBA. Here is a little video on "liquid CO2".

HOW IT WORKS IN A TANK

Curious about how CO2 systems work? Phil explains it to us in the video below. He covers what parts to buy, how to set the system up, and even how much to inject! It will demystify the entire process.

WATCH US SET A CO2 SYSTEM UP

Want to see up put a system together? Let's show you. There are two types we suggest. Paintball tank setups, which are great for tanks that are 30 gallons or less. And more traditional setups that work great for tanks 30 gallons or more. Watch the videos below to watch us set them up.

CO2 INJECTION BROKENDOWN

Co2 is pumped into your tank and diffused into the water column for your plants to take in. There are a couple of ways to do this: the DIY system and the pressurized Co2 system. A DIY system is basically mixing sugar and yeast in a bottle, cutting a hole in the top of the bottle and letting the gasses run from that hole into your tank via tubing. Let me rant for a second and give reasons why I hate DIY systems after using them for years:

There is no way to regulate how much Co2 is leaving the bottle and you could gas your fish
There is no way to regulate the pressure in your bottle and it can explode all over your house. Yes, that happened to me and there are still yeast stains on the wall in my living room.
There is not enough pressure to use it with a good diffuser, and it is unwise to take on the risks of DIY CO2 without good diffusion.
The yeast dies out over the course of weeks, so the amount of Co2 varies over time. At first, CO2 production ramps up, then it plummets back down which creates an unstable environment for your plants and fish…and can cause algae.
Yeast can get into your tank, making it cloudy and harming good bacteria. Again, this happened to me: I think the yeast was so active that it forced liquid up the Co2 tube and into my tank…no fun.

If it is not clear, my opinion is that DIY Co2 is janky, unreliable, and uncontrollable. What is reliable and controllable is pressurized Co2. But I guess to be fair, let me hit the downsides to pressurized Co2.

You may consider having a pressurized tank in your house to be a safety risk since there is a potential for the tank to rupture if it is punctured and/or under too much pressure or heat
It can be expensive
Pressurized Co2 can take up a lot of space
There are lots of different mechanical parts which may be overwhelming if you’re not mechanically inclined.
Your Co2 tank has to be refilled

Pressurized Co2 can sound intimidating, but it’s really not that bad. I’ll walk you through all the gear, how to set it up and how to balance it in your system. Let’s start with the gear. You’ll need the following:

Co2 Canister
Regulator
Check Valve
Bubble Counter
CO2 Grade Tubing
Diffuser (Inline, ceramic, atomizer)
Drop Checker (optional)

1) Co2 Tank – These can be purchased online or at an aquarium store. They come in all different sizes from large 5-10lbs tanks, to smaller 20-24oz paintball tanks, to miniature CO2 canisters used for BB guns. Selecting your size will depend on how much space you have and how often you want to refill it. I like to keep a few 24 oz paintball tanks around so I don’t have to deal with the bulk of larger tanks, but I also don’t have to go have my tanks refilled as frequently.

2) Co2 Regulator – These are what control (or regulate) the flow of CO2 to your aquarium. I suggest using one with an electronic solenoid that can be set on a timer so you can control when it goes on and off automatically. Since plants only consume CO2 during photosynthesis (when light is available), it is a waste of gas to run Co2 when your lights are off. Plus if you run your CO2 overnight, it can build up in the tank and kill your fish or at the very least cause unstable levels of CO2 as it accumulates at night and drains during the day. Most regulators these days have a needle valve built into them so you can control the flow (of how much gas is going into the tank). Lastly, they all have gauges that show you how much pressure is in your reserve tank, and some even show the amount of pressure in your system (including tubing).

Time your CO2 so that it turns on 1-2 hours before your lights are on. This way CO2 saturation levels are high as soon as your light turns on kick-starting photosynthesis. Without doing this, there is a chance that your CO2 saturation levels will not reach an optimal level prior to photosynthesis starting. The goal is to get your CO2 levels up to 30ppm and keep them there up until an hour before the lights turn off

PRO TIP

3) Check Valve – I cannot stress this enough, put a check valve on in your line between the bubble counter (or tank if you don’t have a bubble counter) and the regulator. This allows air or liquid to only flow in one direction. You want air to flow out of your Co2 tank into your aquarium and don’t want water or air going back into the regulator. Naturally, due to siphoning, water is going to want to flow down your Co2 tubing and could potentially ruin your regulator. Regulators are not cheap, I’ve made this mistake, so take care of the one you’re about to get and add a check value!

4) Bubble Counter – This is a visual tool for smaller aquariums (75gal or lower) that helps you gauge how much CO2 is getting pumped into your aquarium... or if we've run out of CO2 and nothing is getting injected into the tank. A bubble counter is a visual indicator that forces bubbles through a liquid or oil to give us an idea of the rate of gas flow in BPS (bubbles per second). The downside with bubble counters is they are not a great tool for dialing our CO2 in. A bubble doesn't tell us how much CO2 is dissolving into the tank. With larger tanks, the flow will be so great that you can't even count the bubbles. We want to hit a saturation target of 30ppm of CO2 in our water column but bubbles is an inaccurate way to measure that. Its best to use the PH method which we will cover a little later. Just know that bubble counters can be a good little visual aid but should be relied on to dial in our CO2 levels.

5) Co2 Grade Tubing – Make sure you pick up Co2 tubing if your regulator does not come with some. It’s the least expensive part of setting up a Co2 system so make sure you get CO2 grade tubing. If the tubing is not CO2 grade, it can leak and deteriorate. The last thing you want to do is set up an expensive Co2 system and have cheap tubing that allows gas to leak (wasting gas and not providing your tank what it needs).

6) Diffusers – There are many types of diffusers; however, the most common ones are ceramic discs/atomizers, inline diffusers, and reactors.

Ceramic discs are the most common diffusers and can come in metal, plastic, or glass housings. They are placed really low in your tank and diffuse Co2 by producing really small bubbles that float around our tanks and tend to be so small that they don’t break the water’s surface (because of surface tension). The thinking is that these microbubbles float around the tank and attach to our plants, bringing the CO2 to them.
Inline diffusers have a higher diffusion rate which makes them more efficient than ceramic discs and can achieve mid to high levels of diffusion. The pressurized Co2 is required to achieve a pressure great enough to break the gas up into a fine mist. This fine mist is shot into the tank and is delivered directly to our plants. Inline diffusers are installed into the outlet of a canister filter, not the inlet, so it can use the flow of our canisters to be delivered throughout our tank.
Reactor – Lastly, we have the most efficient diffuser of CO2, which is a reactor. These trap bubbles in a chamber where they tumble to break up bubbles until they are fully diffused into the water. Then CO2-rich water is injected into the tank. These rectors can be run inside the tank, in a sump, or even in a separate reactor outside a tank.

All of these diffusers are great at getting CO2 into the tank and ready for your plants to take in. Your choice of diffuser should be based on the CO2 demands of the plants in your tank. With that being said, a reactor is always going to be the most efficient way to dissolve the CO2 because bubbles cannot float up and out of the tank, but we don't always have room for them in our tanks, or tank stands. So, we just need to pick which method works for our design and equipment setup.

7) Drop Checker – Drop checkers are a visual indicator of how much CO2 has been diffused into your water column. The most common ones are little clear glass pieces that suction cup to the inside of your tank and are filled with a colored 4dKH solution. The colored liquid changes from blue, which means no CO2, to green, which means an adequate amount of Co2, to yellow which can, but not always, mean too much CO2. The downside to them is that they are not 100% accurate. They can also take about an hour to catch up to what is happening in the tank, which can mean you could have fish gasping for air before it tells you the CO2 is too high. Also, it can be hard for the color blind to read. My thinking is that it’s better to have rough data than no data when you’re first learning. Once you get the BPS set to where you need it, you are generally not going to be fussing with your Co2 and therefore no longer need your drop checker. So if you can afford one, or borrow one from a friend, give it a whirl and see where your tank is at. If not, this is something you could go without. Regardless, we'll want to dial in CO2 saturation levels with the PH method below.

Now the nice thing is the gear I’ve listed above is listed in the order of how the system is designed. You have your source of Co2, which runs through a regulator into your Co2 tubing, through a check valve so water doesn’t backflow, then into a bubble counter, and finally, into the diffuser or reactor to the tank. It’s really that simple.

WHAT ABOUT LIQUID CO2?

Getting the right amont of CO2

GETTING THE RIGHT AMOUNT OF CO2

Once you have your equipment set up, we will need to dial it in to make sure we are hitting the target of 30ppm of CO2 in our water column PRIOR to your lights kicking on. Once we hit 30ppm, then the light can come on. We know a tank has around 30ppm of CO2 injected in it because its PH will drop by one point. For example, let's say we have an aquarium with a PH of 7.8 and have had no CO2 injected into it. If we start injecting CO2 till the PH hits 6.8, this lets us know we've hit our CO2 target of 30ppm. So here is what we need to do to dial that in:

Take a PH reading in the morning with the lights off and no CO2 injected into the aquarium. For example, we'll say I took a PH reading of 7.2
Run your CO2 at 2-3 bubbles per second if you have a bubble counter, if not, look at your method of diffusion and set the CO2 at a level where there is a nice amount of microbubbles coming out of your diffuser.
Let the CO2 run for an hour and then test the PH again. If you hit a PH of 6.2, then you are injecting enough CO2 and you're done! Your lights can come on after 1 hour of CO2 injection. If you're only halfway there, you either need to turn up your CO2, or let it run for 2 hours instead of one and test again.
Once your figure out how much time or CO2 you'll need to inject, then you can schedule when your light come on. So if you know it takes 1.5 hours to drop your tank's PH's to 6.8 (or whatever number drop your PH a full point) then schedule your CO2 to come on 1.5 hours before your lights do.

Photosynthesis is more aggressive in the first 2-3 hours, so we want to make sure our levels are where they need to be right when the lights turn on. Things that can prevent your PH from dropping is a high KH. So if you have a KH of 8+, then it might take longer to hit that 1.0 PH drop. Also, if you turn your diffuser up too high, your bubbles could be shooting up to the top and out of the water tank. This is an indication that you need a larger diffuser and yours is too small, or you're running too much CO2 through the diffuser.