How to Set Up an Aquarium CO2 System the Easy Way

When it comes to planted tanks, we always encourage beginners to start with easy, slow-growing plants that only need low lighting and an all-in-one fertilizer. However, certain plants are a little more difficult to grow underwater and may require high lighting and extra carbon dioxide (CO2) beyond what is naturally provided in the air. When it comes to injecting CO2 gas into water, aquarists have tried all kinds of techniques, types of equipment, schedules, and dosage amounts to put together their own custom DIY systems. Aquarium Co-Op has tried many and created this guide to help you choose the most reliable and simple method.

Can CO2 be used to get rid of algae? This is a common misconception. A healthy tank should have three components: lighting, fertilizer and carbon dioxide. CO2 is not the only primary ingredient that plants need in order to grow. Too much light and fertilizer is common among beginners. Adding CO2 to the aquarium can balance it. If a tank is over-lit or has too little fertilizer but not enough CO2 injection, algae can form.

Let’s look at a cookie recipe for an analogy. You can increase the flour by adding 5x more (e.g. fertilizer) to the dough. Then you will need to multiply the other ingredients (e.g. lighting and CO2) by 5x. This will produce a larger batch of cookies, which will lead to greater plant growth. You can make a bad cookie if you only add 5x as much flour to your recipe.

Does every aquarium plant require CO2 injection? All aquatic plants use CO2 for their basic building blocks. While some types, such as cryptocoryne, don’t need extra CO2, other plants like scarlett temple may benefit but won’t. A third category of plants – which includes Blyxa japonica, dwarf hairgrass, and dwarf baby tears and other similar carpeting plants – has higher demands and necessitates the use of CO2 for the best chances of success.

Materials for a CO2 Systems

This guide will focus on how to install the CO2 system, not lighting or fertilization. Get the tools and equipment you need to get started.

1. Aquarium Co-Op CO2 regulator What’s a regulator? It is a device that controls how much CO2 exits the CO2 cylinder tank into the aquarium water. What’s the difference between a single stage and a two-stage regulator? A one-stage regulator lowers the gas pressure in the cylinder in one step. However, a two-stage regulator lowers the pressure in two, which results in a more reliable and stable flow of CO2. Two-stage regulators are also better at preventing “end-of tank dumps,” where a CO2 cylinder that is nearly empty may leak its remaining gas in one step. Is it better to use a DIY or pressurized CO2? We’ve tested many DIY systems that contain yeast and citric acid. However, they are less stable than a pressurized CO2 system with a regulator/cylinder. The DIY reactions often make lots of CO2 at the beginning and then decline over time, and the inconsistent amounts of CO2 can make it difficult to balance a planted tank. The process can be slow and difficult to maintain because the pressure is lower, the temperature can influence the reaction, as well as the time it takes. A pressurized system is easy to set up and run for one to three decades before refilling the cylinder.

1. Aquarium Co-Op manifold add-ons – You can add up to five additional manifold blocks to your regulator to expand the system or run CO2 to multiple tanks.

1. CO2 cylinder tanks – Is it possible to use a CO2 paintball tank? They work with standard cylinder tanks that have the male thread size CGA320. I need a CO2 tank. We buy ours from local welding supply and home brewing stores. If your cylinder is empty, most stores offer CO2 refill service. – What size CO2 cylinder should I get? If you are running a high tech planted aquarium injected with high amounts of CO2, people recommend getting the largest size possible so you will not have to refill the cylinder as frequently. For the average customer, however, we recommend a 2.5-5lb. A 5 lb. cylinder is recommended for aquariums up to 20 gallon. cylinder for 25- to 40-gallon aquariums, and a 10 lb. cylinder for aquariums up to 55-gallon. You can use one regulator for five to six aquariums. If so, you will need to scale up the cylinder size.

1. What is the difference between airline tubing and CO2 tubing? We use Aquarium Co.Op’s flexible black PVC tubing on all our aquariums. There has been no perceptible CO2 loss. Our experience shows that special CO2 tubing costs more, is harder to bend, and is not as easily available.

1. Regular check valve or stainless steel check valve (optional) – Do I need a check valve for my CO2 system? Check valves are used to prevent water from flowing out of the aquarium and pouring all over the regulator when it is turned off. The Aquarium Cooperative regulator has a built in check valve. However, you can also add another one to provide additional protection. We have personally used the regular plastic check valves with CO2 systems at our fish store, warehouse, and homes, and they have not broken down. However, plastic can be degraded by CO2 over time so we offer stainless steel versions for better durability.

1. CO2 diffuser – Which type of diffuser should I get? Any CO2 diffuser intended for aquariums that can operate at approximately 40-50 psi should be fine. What can I do to clean a CO2 diffuser that has become clogged with algae? Diffusers are made from different materials so make sure to follow the manufacturer’s cleaning instructions. You can use vinegar or bleach or any other method.

1. You can fill the bubble counter with regular tap water or mineral oil. This will allow you to see the CO2 entering the aquarium at an approximate rate. However, the water will evaporate over time, so mineral oil can be used instead so you never have to refill the bubble counter.

Electrical outlet timer 1. Adjustable wrench of at least 1.25 inches width Scissors Spray bottle with water and a few drops of Dawn dish soap

How to Install a Co2 System

Once you have all the equipment, we recommend you follow our detailed manual and video tutorial for step-by-step instructions. This high-level diagram will help you see the whole CO2 system.

The regulator (B), which screws onto the CO2 tube (A), is shown in Figure 1. The regulator (B) can have optional manifold blocks added. The bubble counter (C), located on the regulator, is filled with liquid. An airline tubing attachment is made to the bubble counter’s lid. – The airline tubing connects to the diffuser (D), which is placed at the bottom of the aquarium. – The optional check valve (E) is installed in line with the airline tubing near the aquarium rim. – The regulator’s solenoid valve cable (F) is connected to the power adapter (G). The power adapter, (G), plugs in to the electrical outlet timer H. This plugs into a power strip or wall outlet.

Is it bad if the CO2 bubbles from the diffuser are reaching the water surface? No, this is normal. The key is to place your diffuser as low as possible in the aquarium. The bubbles released from the diffuser will imperceptibly shrink as they rise, and the CO2 gas is being absorbed in the water.

Place the diffuser at the base of the aquarium to give the CO2 bubbles a longer time to dissolve into the water.

How much CO2 should you consume?

In the manual, we recommend tuning the regulator to approximately 1 bubble per second (i.e., the rate of CO2 bubbles flowing through the bubble counter) because we would rather start with a lighter amount of CO2 to keep the fish safe. That being said, CO2 dosing amounts are different for every tank, and the bubble rate is not a perfect form of measurement since each aquarium has different plant and fish stocking levels. Drop checkers are not used to achieve the ideal CO2 concentration, as we prefer to let the plants and nature tell us when they feel happy.

The plants photosynthesise during daylight hours and consume carbon dioxide. They also produce oxygen (O2), and sugars.

If plants have enough carbon dioxide and light, they can produce enough oxygen to saturate the water. This is visible as small bubbles appearing from the leaves. In our warehouse, we dial the CO2 level on our plant-holding aquariums until we consistently see this “pearling” effect. It takes plants 24 hours to adjust the CO2 level. Therefore, we wait three days to make any changes to the system.

Aquatic plants “pearl” or visibly produce bubbles when the water is saturated with oxygen.

When should I turn on and off the CO2 in my aquarium? As mentioned before, plants use CO2 when there is light to photosynthesize. But, this process changes at night to become the respiration cycle. In which plants take in oxygen and sugars, they release CO2. Therefore, we want to shut off the CO2 regulator when the aquarium light is off. To optimize CO2 use, set the regulator’s timer so that it turns on about 1-2 hours before the aquarium light comes on. The regulator will then turn off approximately 1 hour before the light goes out. (If you only have one timer, you can use the same timer with a power strip so that the light and regulator turn on and off at the same time.)

Is CO2 dangerous for aquarium fish? It can be harmful for animals in large enough quantities if (1) CO2 causes the water pH to drop too quickly or (2) people try to be so efficient with the CO2 that they end up cutting off the oxygen that fish need to breathe. Hobbyists may try to reduce surface agitation in order to limit gas exchange and CO2 escape from the water. However, less gas exchange also means less oxygen will enter the water, which can cause your fish to struggle and gasp for air. Use an air stone or other device to agitate the water surface in conjunction with your pressurized O2 system to increase CO2 and O2 levels. Yes, you may have to increase your bubble rate a little to compensate for the slight loss of CO2, but having enough oxygen for your fish (and plants at night) is more important and can help lead to the pearling effect that is so desired by planted tank enthusiasts.

We wish you the best with your new pressurized carbon dioxide system. We hope you have lots of fun exploring high-tech plants. You can find more information about our CO2 regulator on the product page. There is a demo video and a manual.