How to tell when CO2 levels are too low in your planted tank?

Is your planted tank looking a little sick? Is plant growth not right or Algae creeping up?

Operating a high-tech planted tank can be an amazing experience or a traumatic endeavor, depending on your level of skill, attention, and exactly how well you researched your project before starting. When running a planted tank, CO2 levels are very important, as plants use with to create foods, sugars, etc. and when these levels become low, conditions of your tank start to turn south. In order to ensure a safe and healthy living environment for your fish and plants, it is necessary to maintain appropriate CO2 levels. As most of us do not find it easy to clean and maintain our tanks due to the busy hustle and bustle of everyday life, there are some important aspects to focus on in order to ensure a healthy environment for both plants and fish. The gas exchange and oxygen supply in your water could make a huge impact on plant growth and fish health for which implementing a reliable CO2 supply can give great benefits to your tank. To make our readers learn about the alarming consequences of poor CO2 supply, we have thoroughly researched and brought best findings to avoid any future loss.

Why is CO2 important for your aquarium?

Aquatic plants are seriously damaged when CO2 is low or fluctuating in a high-tech tank. Having low CO2 levels can kill plants within weeks if not caught early on. Plants surviving in environments low in carbon dioxide have a much slower growth rate and health that makes it harder for them to sustain healthy growth. Aquariums that have an adequate supply of CO2 will produce results you can visibly notice like, rapid plant growth, better carpeting, and the ability to grow testier plants as well as better colored red varieties. This is all because of the gas exchange that occurs in the planted tank.

In the absence of an artificial CO2 supply, plants have the nature to fulfill the requirements on their own. This method is surely not ideal for aquatic plants as water from the tap will lose its co2 rather quickly. A low tech tank can provide great results when done correctly, but it will not rival tanks with high CO2. Aquariums placed near to a sunlight source tend to grow fast, high light REQUIRES high CO2 and Oxygen.


Creating the perfect balance

Before setting up a CO2 supply into your planted tank, you must learn about how to create a balance between oxygen and carbon dioxide, in addition to meeting other water requirements. It is very hard to overdo oxygen in a planted tank. We recommend creating as much flow as possible without stressing the fish or plants. Each specific plant comes from a different geographical region and sustains itself in its appropriate wild habitat and environment. Some require a high lighting source whereas others growth depends on proper nutrient dosing. Plants are very adaptable though given time, and given proper conditions should adapt. In order to create a perfect balance between CO2 and oxygen, we recommend turning up CO2 to the highest level possible without stressing your fish. Remember, you can only provide high CO2 in excess of 30ppm if you have excellent flow and oxygen. Oxygen can be increased by using a sump or causing as much surface agitation as possible. If your fish are swimming to the surface and gasping for air, turn down the CO2! A dual stage regulator provides you with the ability to fine tune CO2 to their optimal levels.

We highly recommend Greenleaf Aquarium CO2 Regulators.

When properly monitored, CO2 can bring no harm to fish and plants in your aquarium and can actually help your tank thrive.


Along with a regular CO2 supply, aquarists must also focus on adding nutrients to their tank through Estimative index dosing to ensure everyone in your tank is happy and satisfied, but you have to make sure to monitor dosing as well. Unless you can see visible effects of excessive CO2 supply, you can start to increase the supply level each day and regularly monitor it, to ensure levels are balanced properly. Check out the chart here, to help dial in CO2. Keep in mind that in general, the greater the CO2, the better. The only reason to reduce CO2 is if fish are stressing or you have the tank dialed in and are seeing the results you want. In order to keep your aquarium safe from bacterial and other infections, regular maintenance and proper care is mandatory, so making sure you have enough time to start a planted tank, is a deciding factor before beginning. Make sure you do not use any sort of chemicals or detergents to clean your tank, or you will definitely be sorry, as they can cause serious unwanted effects on plant growth and fish health. Planted tanks like stability and consistency. Consistent, stable CO2 is key to plant growth. If you are constantly fiddling with the CO2 bubble counter, this could be the issue! Plants do not like CO2 fluctuations. If you see brown beard algae, this could be an indicator of inadequate CO2 levels. BBA like to hang around the 15ppm CO2 range.

How can you check for low CO2 levels?

To measure the amount of carbon dioxide in your fish tank, KH and pH level tests can be performed, using a water kit purchased from your LFS and on your own. Although a rapid decrease in plant growth is a visible characteristic to watch out for, due to decreased CO2 levels and conducting these tests can help you in evaluating gas concentration to make sure the water is balanced. Furthermore, most aquarists also purchase equipment to make this injection of CO2 easier, such as CO2 regulators and PH monitors to monitor carbon dioxide levels. So, if you see visible signs of low CO2 in your fish tank, using equipment will surely help you catch things before it gets out of hand. CO2 tests can be conducted on your own; there is no need for any kind of professional assistance to complete the testing procedure. To give you an idea, we keep our tanks very oxygen rich with a wet/dry filter sump. This amount of Oxygen lets us reduce the Ph by about 1.5 every day with a KH of 1. At night, oxygen is restored via the wet/dry filtration, and Ph steadily increases throughout the night and by morning is ready for the CO2 to turn back on. If you don't use a sump, we highly recommend using an airstone at night to bring the Ph back up before the next day.


Expected CO2 range and supply

When searching for the adequate CO2 supply in an aquarium, minimum quality levels should be around 30ppm. As these readings can also vary according to your fish tank environment and water cleanliness, make sure the pH Levels inside your aquarium follow your tank requirements, and in most cases, a pH range of 5-7.5 is sufficient for a range of livestock. Remember, raise pH at night and lower it during the day. If your tank is suffering from low CO2, your managed biosphere will suffer, and your role as caretaker will be a complete disaster. Make sure you know what your tank’s needs are so we can avoid letting our planted mates down, and we also can’t forget our fellow swimmers and inverts.

Selecting the best aquatic plants

With the never-ending plant types and categories, it has become quite a difficult task to make a final decision, especially when wanting to stick out from the general layouts and designs. Each of them features unique CO2 and nutrient requirements; proper research is needed to ensure proper plant selection is made when designing your planted tank. One that can thrive in your provided parameters. Check our Knowledge Base for plant ideas. Descriptions and images are added to help aid you. This will surely make it easier to manage the aquarium by yourself in order to ensure better health and growth of aquatic plants. Even in low-tech tanks, CO2 needs to be monitored, and your fish/plant selection will play a big role in your tanks success here too.



Successful planted tanks and aquascapes can be done with no additional CO2 injection required, but the use of reactors and diffusers is becoming a general sighting, so this increases the level of technical knowledge is highly beneficial. Those with CO2 implementing gear will need to have regular and routine maintenance regiments to ensure adequate care for the quick growth of aquatic plants under CO2 healthy environments. The key to everything is a balance, stability, and consistency. With balance plants find harmony.

Rate This Article: