1 Filtration2 Carbon Dioxide (CO2)3 Bright Light4 Substrate 

Carbon Dioxide CO2

Most plants require a relatively high carbon dioxide (CO2) level for photosynthesis. Since there is not enough CO2 in a conventional aquarium, it needs to be added. CO2 system components and assembly are also explained here. 

Photosynthesis by plants requires CO2. The CO2 typically found in an aquarium is very low for plants.  It is hard to keep plants healthy and thriving under these conditions. This problem can be remedied by dosing CO2.

Because of CO2 injection, aquariums can be illuminated brighter, achieving more vibrant color, growth, and effects. Plants will be healthier while having better color and beauty. The aquarium will start to “pop” with fresh colors.  CO2 will open up a new world of aquarium keeping, transforming a tank into an art piece. If keeping a natural, living aquascape is the goal, it is definitely worth investing in a CO2 system.

Why is CO2 necessary?

Aquatic plants photosynthesize when their leaves are exposed to light. To do this, they use the nutrients and CO2 in the water to produce glucose and oxygen. Aquatic plants use glucose to grow. Oxygen is released from their leaves during the process, used by fish and other microorganisms in the aquarium to breathe. CO2 enters the aquariums naturally from fish and microorganisms. If the aquarium is heavily planted – under intense lighting, the plants will consume the CO2 quickly and deplete it. The depletion of CO2 in the water causes plants to stop photosynthesizing. If such conditions exist in the aquarium, the plants will not thrive. On the other hand, if fewer plants are in the aquarium or the lighting is dim, it is not necessary to dissolve a large amount of CO2 in the water. Sufficient CO2 must be dissolved in water to uniformly photosynthesize plants and create the “Nature” look with heavy plant loads and no algae.

How much CO2 should be added?

The ideal level is 30 ppm (mg / liter). 

The 30 ppm (mg / l) CO2 level has no detrimental effect on fish health. However, be careful not to exceed this level for an extended time because fish can quickly die from CO2 poisoning. The first sign is that fish twitch near the water’s surface. This phenomenon occurs because too high a level of CO2 also increases the oxygen demand of fish. Greater oxygen concentrations will exist on the water surface due to gas exchange. The second, more severe symptom of CO2 poisoning is when fish move erratically back and forth in the water, sometimes swimming upside down and visibly losing their ability to orient themselves. It is more difficult for them to recover from this condition, and some may perish. A quick change of water and aeration may still save some of the stock.  Use an air pump with an air stone temporarily. The third phase is typically fish death.

If the CO2 is adjusted properly, there is no danger to the livestock. When observing the aquarium, keep in mind that the CO2 level is closely related to the water movement in the aquarium. If the CO2 level is around 30 ppm when using a newer clean filter, this level will increase as the flow slows down and problems may occur. Reduce the number of CO2 bubbles if the filter is not cleaned regularly.

“When I was young, I loved whiskey with soda. (…) One night I went to the pub with a friend and ordered whiskey with soda as usual. The counter was in front of me—a glass of whiskey with ice and a bottle of sparkling water. The sparkling water sparkled as I poured it into the glass of whiskey, and the air bubbles danced in it. I involuntarily picked up the bottle of sparkling water and looked at it. This immediately slammed a string inside me. I knew it was the breakthrough I had been waiting for in my aquarium projects. I bought all five bottles of mineral water from the pub and ran home, pouring them into an experimental aquarium.” – Takashi Amano (1954-2015)

John Tullock on CO2 This a a post of John Tullock regarding carbon dioxcide.

What are the CO2 injection methods?

The first Method is when there is no gas CO2 system used, the only good solution is to use the treatment Evoke for plants, which contains “carbon-based” compounds in a form that can be taken up via the cell wall. This also helps prevent excess algae. Use Evoke by aquaLife for this method. We are not suggesting this is a direct addition of “liquid carbon” or CO2 as many manufactures suggest but rather a method that does work for various reasons and helps with algae.

The second method is the use of yeast CO2. This homemade method can achieve results similar to high-pressure CO2 systems. Still, their reliability is very low, and the gas cannot be shut off overnight, which is essential. Combined with mess and inconsistent results, this is the least desirable method.

The third method is using tablets, such as those by Azoo and Sera. This only works for smaller (nano) aquariums. Tablets have to be used daily and cost more than CO2 systems long term. 

The fourth method, and the only one that works without compromise, is the use of high-pressure systems. Versions are available for smaller (nano) aquariums and large aquariums. 

“Plenty of methods have been used to dissolve CO2 in an aquarium. The best method today is direct dissolution – which is safe and effective. Use a gas cylinder to source CO2, which contains liquid carbon dioxide. Combine it with a high-quality regulator and a needle valve, which reduces the pressure and creates a steady CO2 flow from the cylinder. The CO2 from the cylinder passes through the needle valve, best used with a solenoid valve so it can be switched on and off. The gas then often passes to a tank-mounted check valve and bubble counter. Using CO2 pressure tubing, connect it to another check valve and a glass bubble counter. Use glass or stainless CO2 diffusers, like those from Hydra Aquatics of VIV, to dissolve the CO2 in the water.” Aquamanknox 

CO2 Bottle (or cartridge)

It is typically 95g to 5lb in size. For some regulators, paintball tanks can also be used with adapters, such as the Hydra Aquatics model. 

Regulator Hookup

CO2 Regulator

The pressure of 50-80 bar in the cylinders is reduced to a manageable pressure of 20-70 psi. The bubbles (CO2) volume can be controlled with a needle valve mounted on the regulators. See this Video for regulator best picks.  If you want to know everything about regulators, how they work, and hookup, see this video.

What is needed after the regulator

Diffuser and what is needed for CO2 hookup

CO2 Solenoid Valve

At night, plants do not need CO2; the solenoid valve connected to the light timer shuts off the CO2 gas. During the day, inject at least 2-3 hours before turning on the lights or when the lights come on. If a second timer is used, it is advisable to stop them together with the lights.

CO2 Tubing

It is advisable to use pressure-resistant tubing suitable for CO2 to prevent problems.

CO2 tubing Types

CO2 Check Valve

The Check Valve prevents the aquarium water from flowing back through the CO2 pipe when the CO2 is switched off. If water flows back, it can damage the solenoid valve or regulator. Water could also possibly leak onto the floor.

Bubble Counter

The amount of CO2 injected into the aquarium can be adjusted using a needle valve. A bubble counter shows exactly how much CO2 will get into the aquarium. The right number of bubbles depends on many things. Start with one per second.

CO2 Diffuser or Reactor

CO2 gas is injected into the aquarium water through a CO2 diffuser (ceramic “atomizer”) or reactor. The diffusers are made from glass, acrylic, or stainless steel. Reactors can also be used in larger aquariums. 

Diffuser Selection

The most significant difference between CO2 systems for more extensive and smaller aquariums is the size and or quantity of the diffusers, which dissolves CO2 in the water. The size of the diffuser is determined by the diameter of the ceramic atomizing disk in the diffuser.  As the disc size increases, so should the aquarium. For example, a 30mm diameter disc is suitable for a 24-inch long aquarium, a 40mm diameter for a 48-inch aquarium, and a 50mm diameter for a 72-inch long aquarium. Choose between diffusers in the glass or stainless models based on placement and appearance. VIV and Hydra Aquatics make the best models, while UP Aqua makes high-quality, lower-cost versions.

For sumps and larger aquariums, reactors or atomizers like those by Mr. Aqua are very efficient.  They use a pump to churn the COand force more into the water column.

CO2 Drop Checker

The most effective tool for measuring CO2 at home is the drop checker. The dissolved gas discolors the indicator solution in the small glass bell. Blue = low, green = adequate, and yellow = too much CO2.

Other recommended accessories for a high-pressure CO2 system:

pH test – preferably in drop test type (non-paper)

Replacement seal (sealing ring) for the CO2 regulator. It is not expensive, but it should always be on hand.

View Drop Checkers

Also See Carbon Dioxide Part Three Installing A System

How to measure and determine Carbon dioxide levels in the aquarium.

Regulator Installation and Instructions

CO2 Glassware with Video Hydra Aquatics

We have included frequently asked questions about CO2 including cleaning and choosing diffusers here.

1 Filtration2 Carbon Dioxide (CO2)3 Bright Light4 Substrate