How To Setup And Dial-In Co2 Properly Without Killing The Fish

There is an art to learning how to dial-in CO2 into an aquarium without killing the aquatic fish and

There is an art to learning how to dial-in CO2 into an aquarium without killing the aquatic fish and plants. The overall goal is to determine and maintain the optimal balance between the varying elements of the tank with the appropriate levels of CO2. Most people rush into the process without fully comprehending how these underwater biocommunities operate and how the elements are intertwined. Nevertheless, once you understand the process, you will have a flourishing aquarium that will be stunningly appealing.

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Sifting Through the Sea of Online Information When Honing CO2

Online, you will find a vast amount of conflicting information regarding the addition of CO2 to your planted tank. Some reports suggest that 30 ppm of CO2 is optimum for aquamarine plants. Others will proclaim that the most efficient measurement is the appearance of green on the drop checker, and that maintaining that that color is the detrimental goal. Moreover, others will instruct you to utilize the pH controller and stabilize the pH levels in order to achieve the optimal CO2 level that the plants require. Nevertheless, even with the abundance of information available, there are very few who provide instructions on how to dial-in CO2 without overdoing it.


On your search for information, one of your biggest concerns will be the concentration of CO2 that is available to the plants daily. You are not looking to achieve a certain number because not all plants and arrangements of aquatic life respond the same to individual measurements. Instead, there is an ideal range that you should aim towards as those are the levels that have proven to be most optimal. Overdosing the water with CO2 will quickly kill your fish and plants, so it is vitally important that you adjust CO2 levels gradually. In order to discover and achieve the optimal CO2 level, there are a few daily guidelines to follow.

Sufficient Method Of Delivery


The art of fine-tuning your CO2 delivery methods will require that you have a reliable CO2 regulator. You also need a solenoid valve that controls the on and off positions of the needle valve. The needle valve is the most important component of your system, as it will allow you to make fine and incremental visual adjustments most effectively. If you fail to invest in a sturdy and resilient needle valve, your adjustments will not steadily hold, and your bubble count will constantly drift, forcing you to adjust the needle valve constantly. Your main objective is to attain consistency with the bubble rate, which will empower you to be able to find the most efficient CO2 level to dial in to.

Getting Close To Your Optimum Target


Even though the totality of the experience will be different for each individual hobbyist, just about everyone who is looking to dial-in CO2 into their aquarium will take identical initial steps to get the process going. First, you want to begin the process of injecting CO2 into the tank, starting at a very low level and adding a pH controller or kH drop checker.

The key is to keep the kH level consistent once you achieve the correct concentration. This will help you to estimate roughly how much dissolved CO2 is in the water, which you will need to closely monitor now, and as you move forward every step of the way. You also need to maintain a constant delivery of CO2 while maintaining constant kH levels simultaneously.

Keeping kH Constant

When we refer to the kH levels in the water, we are talking about the carbonate hardness of the H2O. Hard water will minimize pH variations and fluctuations. That way, as you add additional CO2 to the water, the pH level will buffer and not immediately, respond by rapidly declining or in the case that the CO2 supply is terminated, resulting in increasing too fast. For optimal effectiveness, aim for a kH level of 4 or 5 dKH, which appears to be an ideal range for most aquatic ecosystems.

Measuring Dissolved CO2


Even if you have a way to effectively control the fluctuations of the pH levels in the water, you still need to measure the amount of CO2 that is dissolved in the water. Even if you do not have a highly accurate CO2 measuring device, you can still adequately determine if the plants are receiving the correct amount of dissolved CO2 that is needed in order to meet their needs by using the drop checker.

The liquid inside the vial turns colors that provide a visual representation of the pH level of the aquarium water, with green being the color that proves to be most cultivating for the plants. By maintaining the green color on the indicator, you will have made a significant accomplishment that propels you one-step closer on your journey of dialing-in CO2 without deteriorating your tank’s ecosystem.

The pH controller can also be utilized to measure the CO2 concentration. While it is not an accurate way to gain a CO2 assessment, you can acquire an approximation of CO2 levels by taking note of the kH and pH levels; using a chart to compare them in order to determine the current CO2 range.

Learning the Art Of CO2 Dial-Ins

At this point, you will have achieved a CO2 concentration level that is suitable for your plants, but it is not optimized just yet. Instead of taking direct action, your task now is to take close observation of your planted ecosystem as you very gradually increase the CO2 levels. You want to go higher and higher in very small increments until you reach a level that begins to diminish the environment.


What To Look For

While it does take experience for you to know exactly what you are looking for, there are generalizations that will give you an idea of the changes you must be able to identify when you are officially dialed-in. The plants should have a bold and vibrant color. Their size should expand, and their growth should appear to be rapid and evolving. Newly sprouting buds should be the correct size and display the proper colors.


Tiny gas bubbles should pearl and emerge from the plants during their illumination period. The increased oxygen concentration in the water should make the fish vibrant in color, highly active and hungry to eat food when placed in the tank. The water in the aquarium should be crystal clear, without any sign of cloudiness or algae, while giving off a fresh smelling aroma.

How To Properly Dial-in Additional CO2

At the beginning of your CO2 release cycle, your needle valve should he turned one-quarter of the way. This should be on day one. After a few hours of allowing the CO2 to flow, check to make sure the drop checker is still green in color and that nothing looks out of the ordinary. If the drop checkers color is leaning more towards yellow, the CO2 concentration may be too high, so it is important that you keep a close watch on the aquarium inhabitants for any signs of distress. If you do notice distress, decrease the gas flow by 1/8th of a point and keep a watchful eye on the color change on the checker.

Before making any additional adjustments, give the aquarium about three days to settle in the new environment. Once that period has passed, you can further adjust the CO2 levels by turning the lever in quarter turns. Keep making those increments in turns until the water starts to decline in quality. That is when you know you have achieved your most optimal point, and you should turn back the valve to its previous setting.

While this process may seem labor intensive, rest assured that this process will help you know how to dial-in CO2 efficiently, without killing off the fish, plants and other inhabitants of the aquarium. In the end, the water will be clear, the fish will be vibrant, active and healthy, and the plants will flourish. By rushing the process, you will not accelerate the ecosystem’s progress. In fact, you will do the opposite. Halting its growth and in commonly severe cases, killing fish and other aquatic residents of your planted aquarium.

Eventually, you will not need a drop checker or a pH controller. Dialing in CO2 can be an easy process if you follow these simple rules:

1. Have as much flow as possible without stressing fish/plants

2. Make sure there is a lot of water ripple on tank surface. Having moving water at the surface is similar to putting in an airstone (except without the unsightly look.) Ever see plants pearl like crazy? This usually happens right after a water change or when there is excellent surface ripples providing full oxygen to the plant roots

3. Increasing O2 allows you to increase CO2! You can easily push past the typical 30ppm drop checker if you have high oxygen in the tank. When the solution turns yellow, it doesn't mean the CO2 is too high; you just need to make sure you have enough O2 to protect your fish.

4. Start your CO2 low and continue to crank it up. BPS is relative to individual tanks and shouldn't be relied on at all. To get an idea, a pH drop of about 1 full pH in a tank with a kh of .5-1 will be about 30ppm of CO2 as a good starting point.

5. Get a good diffuser. If your CO2 is high, but you are not seeing results, make sure you are diffusing properly. The typical ceramic diffusers may have a hard time reaching the opposite end of the tank. Green Leaf Aquariums makes an atomic diffuser which has much finer micro-bubbles and gets all around the tank. Placing a powerhead above the diffuser can also help spread it properly.

Still having issues with CO2? Send us a PM, and we will be happy to help.


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