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CO2 Injection Aquarium

CO2 Injection Aquarium

CO2 injections typically take place in planted tanks, otherwise known as planted aquariums. They differ from standard aquariums in that plants are the primary focus, with fish playing the role of the supportive backdrop. 

Plants survive on carbon dioxide, releasing oxygen as they grow, creating a circle of dependence between plant life and ourselves. Injecting CO2 into planted tanks has a dramatic and rapid effect on the robustness of your plants, providing them with the necessary glucose conversion they need. 

Injecting CO2 is a balancing effect. When the plants in a planted tank get too much light, their CO2 accumulations drop. Injecting CO2 returns the balance between energy through photosynthesis and the utilization of that energy to convert CO2 to glucose. 

How Do You Inject CO2 Into a Fish Tank?

There are two methods for injecting CO2 into a pressurized tank. The first is a DIY (Do It Yourself) ordeal and the second is a pressurized system (or CO2 kits) The latter is easily the most popular. That’s because CO2 kits are much easier to regulate and you can turn them off when they’re not in use. 

Pressurized CO2 Systems

A pressurized system comes with a CO2 tank that has a pressurized valve on the top so it’s easy for you to release CO2 whenever you’re ready. This is the easiest way to go about keeping up with the carbon dioxide levels in your planted tank system. 

You can essentially set it to what you want and keep it that way, without having to mess with it, until it’s time to refill the tank. For instance, a 5lb CO2 canister will go perfectly with a 30-gallon tank.

Another benefit is that you can easily control the rate of flow. It’s not something that you just switch on and off at your leisure. You set the rate of flow and walk away. Many of these CO2 kits will release CO2 based on a timed system of release. It just depends on how high-tech the system is when you purchase it. 

These kits come with multiple chambers (cups), the CO2 cylinder, a regulator with a pressure gauge, a bubble counter, and a diffuser. The cups go into the water and the diffuser sits at the top of the cups. As CO2 is released from the canister, the diffuser emits the CO2 into the cups, where it slowly fills up, releasing a little bit at a time into the tank. 

DIY CO2 System

A DIY method is going to be set up in a similar fashion, and you will need a diffuser to deliver the goods into the tank. You will use a 2-liter plastic bottle and tubing that will run from the bottle into a check valve. 

From the check valve, additional tubing will run to a gas separator, which is a 20oz plastic bottle. The 20oz bottle will have an ingress for the tube coming in and egress for another tube going out.

The tube going out of the 20 oz bottle will run to your diffuser, which goes in the tank. In the original, 2-liter bottle, you will either have to create your own yeast through a fermentation process that releases CO2 or purchase the stuff to pour into your bottle.

Is CO2 Injection Necessary for a Planted Tank?

You may not need to. It just depends on how much or how little the light is for your planted tank plants. CO2 injections boost the level of growth. It’s recommended for most planted tanks and especially for planted tanks that get a lot of light. 

It also depends on the kind of plants you are growing. Some plants have different light needs and are more responsive to direct CO2 injections, so it makes sense to give it to them. If you just want really vibrant, strong, and healthy plants, CO2 injections are necessary to get them to that level. 

CO2 injections are going to give you the most successful plant growth success in a planted tank. This is true even if your plants are getting low levels of light and prefer low levels of light. 

How Much CO2 Should I Inject Into an Aquarium?

It depends on how much CO2 your plants need. If they are receiving low levels of light, they won’t have the energy to convert too much CO2. If they are getting a lot of light, you will see an incredible difference when you introduce carbon dioxide to the system.

There are two tools that you can use to monitor and tune down or up the level of injected CO2. The first is a drop checker, which is a strangely shaped glass holder with a liquid inside of a spherical holding tank. The color changes based on how much CO2 is passing through and into your tank.

Knowing the colors will tell you the level of CO2. The second is a bubble counter. Each bubble that pops up at the bottom is a bubble of CO2. How many bubbles pass through per second is how you measure the CO2 outflow. 

Does CO2 Injection Harm Fish?

It certainly can if it’s too much. The plants will take care of the CO2 levels in the tank and release the oxygen that the fish need. However, if you’re pumping more CO2 into the tank than the plants can handle at once, there will be a negative and suffocating effect on the fish. 

It will drop the pH levels in the tank too, which is something that fish are sensitive to as well. Since we’re talking about planted tanks, there should be enough plants in your aquarium to deal with the CO2, so long as you don’t run it through the roof. 

All Things Considered

Injecting CO2 into your planted tank is an excellent way to improve the health and vibrancy of your plants. Of course, it’s not for every tank, especially low-light planted tanks that are doing well in that kind of environment. 


Unless you’re an expert with DIY equipment, you should purchase a CO2 planted tank kit, especially if you are new to this, as it will help you keep the CO2 flow well-regulated for both the fish and the plants.

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