How much CO2 should I inject into aquarium?


Injecting carbon dioxide into a planted aquarium provides vital elements that allow photosynthesis. This process is necessary for the health of your plants and fish. The amount of CO2 injection required depends on several factors, including the size, type, and depth of your aquarium and its inhabitants. Read on to learn how much co2 is needed to help plants grow effectively and how much is too much.flux co2 diffuser 

What is the best way to inject CO2 into an aquarium?

Like everything else, there is more than one co2 injection aquarium setup. That being said, the most common co2 injection method involves using a pressurized CO2 system. A CO2 tank is connected to one or more diffusers placed in the aquarium, where they can dissolve into the water column. This setup allows for more precise control of how much CO2 is released into the aquarium, ensuring that your plants have access to the desired amount of CO2 for optimal growth. Other methods of CO2 injection include adding baking soda and vinegar or a particular liquid CO2 product. However, the pressurized setup is generally considered to be the best method because it provides more control over how much co2 is released into your tank.

One of the most commonly asked planted tank questions is, how to add co2 to aquarium water? However, many people fail to ask how much CO2 is needed to create a safe but successful planted aquarium.

How to control the flow of CO2 into your planted aquarium?

When adding co2 to aquarium water, you must provide the correct amount for safety and effectiveness. The most reliable and accurate way to achieve this is through pressurized CO2 systems. These systems provide a consistent and measured flow of CO2 into the aquarium, allowing you to adjust the rate based on your needs. This allows for a more stable environment for the plants and fish and better algae control. There are several working parts within a pressurized co2 system, but two, in particular, are essential to controlling the level of CO2 that your aquarium plants receive.

  • Bubble Counter - This provides a visual element to the flow of CO2 travelling from the regulator into the aquarium. CO2 travels into the bubble counter and through fluid which creates a bubble. We can adjust the flow of CO2 and the rate of bubbles by slightly turning the needle valve in the bubble counter. This gives precision control of the amount of carbon dioxide entering the aquarium, and by counting the bubbles per second, we can understand how much co2 is needed for optimum effectiveness.
  • Drop Checker - Once the CO2 travels into the aquarium water, tiny bubbles are produced by the diffuser. The tiny bubbles of CO2 will dissolve within the water column and eventually be consumed by the plants. A drop checker is designed to sit inside the aquarium and measure the level of dissolved CO2 within the water. Using a special reagent fluid, the drop checker can tell us if we have too much, too little or just the right amount of dissolved CO2 in the water. With this information, we can make any necessary adjustments to the flow of CO2 into the aquarium.drop checker

Do all plants require the same amount of carbon dioxide?

Did you know many plant species in our aquariums are not genuinely aquatic? They are land plants that have adapted to live and grow in water. As such, their demands for CO2 may be different from that of truly aquatic plants. Depending on the type and species of plant, they may require more or less CO2 to grow and thrive. Before you add co2 to aquarium water, it is good practice to research your chosen plants and clarify if they require lots of co2 or just a little. This will help you decide how much co2 to add and ensure the plants receive the right amount. Adding more CO2 than required could put your fish at risk, while too little could limit their growth. While researching your plant care needs, you will also learn about the light levels, nutrients and even the best place to position them within the aquarium.

An example of a plant that requires lower levels of CO2 is the anubias. This type of aquarium plant is very hardy and can thrive in a variety of conditions, including low light aquariums which makes it perfect system with lower levels of co2 being injected.

At the other end of the spectrum, a plant species that requires high levels of carbon dioxide is the cabomba. This type of aquarium plant is usually found in deeper water and prefers bright light, meaning this is best suited to aquariums with higher levels of co2 being injected.

What happens when we get it wrong?

Proving the wrong amount of co2 for aquariums can either be harmful to the fish or harmful for plants, specifically the species that require lots of CO2. Planted tanks are contained ecosystems and everything works in harmony, creating a balanced environment. When one part of this ecosystem falls out of place, it has a knock on effect. For example, a plant species with a high CO2 requirement that does not receive adequate co2 will struggle to grow, begin to "melt" away. When this happens, the rotting plant matter becomes a hotbed for algae growth. Algae then begins to consume nutrients and results in other plants loosing out on vital nutrients which ultimately invites even more algae.

Providing a planted aquarium with too much pressurized co2 can not only harm plants it can be fatal to the fish too. Excess co2 will lower the pH level in the aquarium and if this goes on too long, it will eventually damage the plants roots causing development issues and altered appearance.
More seriously however, too much carbon dioxide could kill your fish. Prolonged exposure to 30ppm of dissolved co2 within the aquarium water will, over time cause the death of your fish. High co2 causes a build up of carbonic acid within the water and fish don't react well to this substance. Fish will also show a reduction in activity, behave erratic. You may often find your fish at the surface of the water looking for oxygen.

How can we prevent accidentally injecting too much?

Investing in a quality aquarium pressurized co2 system should not be overlooked in an effort to save money. You can install a safe and reliable co2 system within most budgets and by doing so, you will have all the tools to safely provide your planted aquariums with the correct level of co2. Our CO2 regulators are equipped with a solenoid valve which allows the user to automate the supply of co2 by attaching a wall outlet timer.For the optimum supply of gas and to insure no co2 is left in the aquarium water when plants are not consuming it we recommend beginning the co2 injecting one hour prior to the lights powering up. This creates a healthy level of CO2 in the water, ready for your plants to consume as soon as they begin photosynthesis. Furthermore, stopping the supply of CO2 one hour before the lights are due to be switched off will allow most of the co2 to be absorbed before the plants stop photosynthesis. During the lights off stage (night time) your plants will produce oxygen which is a great way to keep your aquarium nice and healthy.

aquarium plants

Bubble counters have always been a great way to measure the rate at which your co2 system is injecting gas but we cannot rely on this alone for preventing an overdosing situation. Equally, drop checkers can indicate when the level of dissolved CO2 either rise or drop but should not be relied on alone. A combined effort of all the above is the best approach.

It is also recommended to make sure your aquarium has plenty surface agitation. By aiming your filter outlet slight towards the surface, you can create ripples and this will allow for a healthy gas exchange and help to prevent issues such as pH drop. Good surface agitation also prevents a build up of oily substance on the surface which nobody wants to see.


Injecting carbon dioxide into your aquarium will benefit many plants. When done correctly, the benefits are clear to see. However, when done wrong, there are risks. We recommend investing in a reliable co2 system. Make sure to utilize items such as drop checkers, check valve, solenoid valve and bubble counters for a great all-round view of what is happening within your aquarium at all times. When making adjustments to the output pressure, make slight movements of the needle valve and allow time for the aquarium to adapt to the change before making further changes. Like everything else in the aquarium world, we must be patient to get the results we hope for. CO2 injection is a benefit to all aquarium plants as long as the correct level is provided safely.

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