Why is CO2 such a good help when combating algae?

The most common problem a planted tank encounters is algae growth. There are many forms of it. The planted tank first sees Diatoms (brown algae), which occur within just days of the tank is set up and flooded. As the tank slowly matures, it may encounter other algae forms like Hair Algae and Black Beard Algae. If it survives these initial algae attacks, it can contend with Green Dust algae and Staghorn Algae. Most experienced hobbyists already know the simplest and most effective way to deal with this problem- carbon dioxide injection.

This article will not go into intricate details on the life of algae. Instead, the discussion goes straight to finding out how to kill it with what is available in the planted tank. Read on to the end to learn about one of the uses for CO2 that will not only assist your plant growth but provide a solution to defeating unwanted algae growth at the same time. 

algea aquarium


Clean-up crew

There are numerous algae treatments and controls. Some do employ algae-eating fishes, snails and shrimps. They are great, but most algae eaters who have become popular in aquascaping can be considered specialists. Some species only eat one specific type of algae and do not even touch the rest. The best algae eaters, namely Scat Fish and Mollies, do not survive in an aquascaped tank for long since they are brackish water fishes. Even Nerite Snails, mostly known for their ability to eat algae and clean the tank, are brackish water species. However, employing algae eaters do have its limitations, and often when algae occur, it takes hold of the entire tank. This is too much for a handful of fish or snails to overcome. One would also want to avoid getting more algae eaters to fix this issue. Otherwise, the tank will be stuck with unwanted fish that are difficult to feed if algae run out.

black molly

Chemical solutions and UV sterilizers

Numerous chemical products out on the market claim to be able to kill algae. Some gadgets also make that claim, and they would all be effective as a remedy for algae blooms, but no product could prevent algae from returning. For example, UV sterilizers can help eliminate the free-floating spurs but could never really do anything about the ones attached to rocks and wood.


Yes, algae can be destroyed, but understanding why it is there in the first place is necessary for the problem to come back. It is as if all these things are just band-aid solutions to a bigger problem.

So, what triggers an algae bloom?

Algae, in the sense that they manufacture their food through photosynthesis, are considered plants. They may not be regarded as actual plants since they lack the structures most plants have, but they are plants nonetheless. How much CO2 does algae absorb? In most cases, when algae are present, they will consume CO2 at the same rate as actual aquatic plants. The environment that the aquascaper aspires to perfect is also the perfect environment for algae. Bright light and sufficient nutrients needed by plants are also what algae need. The difference is that algae are quicker to reproduce and take over than plants can. So, the planted tank is a perfect grow-out tank for algae. Competition is the only thing to prevent algae from overcoming the whole tank.
In all aquariums, there is a Plant - Algae CO2 capture war and plants are more prominent, so they get the upper hand. The only problem is that while plants are taking the time to adapt and establish themselves in the new environment they were introduced to before they started growing, the algae carbon capture mission is well underway. When algae become numerous enough, the plants begin to become unhealthier.
Unhealthy plants cannot absorb nutrients well, which is good news for algae. The only thing the aquarist can do to win the Plant - Algae carbon dioxide battle is to help the plants establish quicker and start growing while trying to prevent algae from taking over. Once the plants start growing, they will then take over the hobbyist's job of snuffing algae out.

How to fight algae in the first stage of aquarium development?

Many things must be done during the first three months of a planted tank's life, all to prevent algae from taking over.

Start with low light

Most aquarists advise only a partial blast and the entire photoperiod on day 1 to day 7 of the tank. Start at 2 to 3 hours of photoperiod (lights on) on day one and gradually increase it until it reaches 8 or 10 hours on the second week. This prevents the plants from going into hyperdrive with photosynthesis while trying to adapt to the new environment. This is also done to make sure algae does not grow that fast.

Water changes are essential.

Partial water changes should be carried out daily during the first week of the setup. This removes excess nutrients that might leach from the soil or wood. Nutrients in excess are, again, good news for algae.

Carbon dioxide injection

Lastly, CO2 injection is provided for the plants during photosynthesis. Many experienced aquarists say this is the best way to combat algae. It is directly and indirectly true. While algae can also benefit from sufficient CO2, plants are the real benefactors. With CO2 injection, the plant's time adapting is cut in half. But it would help if you were careful with selecting the equipment. Here are the main rules you need to follow if you'd like to enjoy a healthy and efficient carbon dioxide injection:

  1. Search for regulators with second-stage construction to make sure your animals are safe. Nothing is worse than a well-functioning aquarium with a sudden CO2 burst killing all the fish and shrimp.
  2. Set the working pressure to 40 psi if you have a ceramic diffuser. Too low an operating pressure may clog the ceramic very fast, resulting in CO2 deficiencies.
  3. Use only CO2-resistant tubing. Other materials will cause leaks and become brittle over time. Therefore it's best to invest in high-quality tubing that is only a bit more expensive than silicone.
  4. Observe the drop checker, especially if you have live animals in the aquarium. If the reagent's colour turns yellowish, your tank's bubble rate is too high. If you see any fish gasping for air, do the immediate water change, which will decrease the CO2 level.
  5. With well-set CO2 equipment, plants develop fresh leaves and roots immediately and skip the melting part instead of melting and growing new leaves after. A tank with adequate and constant CO2 supply should never see a plant melt, even if it is newly planted. Plants start growing fresh leaves, and the growth rate gradually increases daily with help from CO2. A small tank could have enough plant mass to compete with algae in three weeks. This is the time the tank is now balanced.
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Planted tanks are not the same!

Some may take longer than just 3 weeks to be balanced but in general the Some may take longer than three weeks to be balanced, but generally, the aquarist will know if the tank is already balanced. Plants start to become healthier. Colours become vibrant. All plants will have an overall appearance of life. If everything goes well with the carbon dioxide injection, plants will show signs of pearling by the second week. Pearling is when plants release Oxygen through their leaves. This is a good indicator of photosynthesis, meaning plants are becoming healthier and starting to manufacture their food.

 CO2 never directly prevents algae from growing?

It helps the plants so the plants can prevent the algae from growing. It is an indirect contributor, but one thing makes carbon dioxide one of the best algaecides. One of the effects of carbon dioxide injection in the tank is it turns the tank water slightly acidic. A slight increase in the tank water's acidity can be tolerated by plants. Aquatic plants thrive on it. Most natural aquatic environments where plants can be found have soft, slightly acidic waters. Algae, except for a few varieties, have difficulty thriving in acidic water. They hate acidic water. Studies have confirmed this. Acidification in the ocean water through dissolved CO2, as studied, kills most algae. If this process did not occur, the oceans would have been filled with green algae by now. It is the same with the freshwater varieties of algae. Most fail to thrive in acidic water. This is nature's way of controlling algae from taking over the planet!

Algae thrive on stable pH. Most algae not only cannot thrive on acidic water, but a swing in the pH of the tank water is sure to contribute to its demise. Hi-tech (with CO2 injection) setups do not have a stable pH. Water turns slightly acidic in the daytime, during photosynthesis, as this is the time when CO2 is injected into the tank. At night, CO2 is turned off, and with a bit of surface agitation or an airstone, Oxygen and other gasses are introduced to the tank, which swings the pH back to neutral or a bit higher. Oxygen can influence the pH swing.

A quick note though

Do not tamper with the planted tank's pH by introducing chemical products. Do not try to lower it or make it higher. Instead, provide soft water with TDS(Total Dissolved Solids) of 80-150. This should be sufficient. The CO2 injection, the gadgets used to create surface agitation, and the plants themselves will take care of the rest.


While this subject may be too much to take in, especially for a newbie, knowing this is helpful in this hobby. Until someone can come up with a product that eradicates it and prevents it from coming back with just one application, algae are now aquascaping's number one enemy. It destroys the precious designs and chokes the plants to death, not to mention it discourages the hobbyist. Many have quit just because of it. If any, this is the number one obstacle the hobbyist needs to overcome. This is what prevents us from enjoying our hobby. Be okay with being good at designing the tanks or getting the most popular equipment. Learn how to avoid algae blooms first, and the rest will follow. Always remember the algae co2 absorption rate is the same as your plants. Focus on maintaining many healthy plants that will outcompete the algae for nutrients.
No matter how simple the design of the tank, no matter how standard the plants and hardscape are being used, and how cheap the equipment is, a planted tank will always be eye-catching if the plants are happy and healthy.

Any questions? We are always happy to answer them! Feel free to contact our Customer Service via support@co2art.us anytime!