Is Co2 tablet effective in a planted tank?

Once you have designed your home aquarium, chosen your fish, plants, and other creatures you may think that the hard work is over, but this is not the case.

In fact, you will need to make sure that your tank is always kept in a good condition. This will involve regular cleaning, maintaining water conditions, and keeping particular species under control (due to high reproduction rates).

One of the most important things that you will need to regulate in your home tank is the gas levels. This involves predominantly oxygen, nitrogen, and Co2.

Why do you need Co2 in a planted tank?

Co2 is the single most important element in a planted tank, so you should be very aware of its levels in your home aquarium. 

This is because Co2 is vital to the well-being of your aquatic plants. They need Co2 to grow and to breathe. Many people are well aware that plants make their food through a process called “photosynthesis” but are you also aware that this involves carbon dioxide?

During the day your aquatic plants will need an almost constant supply of carbon dioxide in order to breathe otherwise you may find that they suffer as a result of insufficient levels.

If you find that your plants are doing just fine without any adjustments to the Co2 levels, then great! You will not need to adjust this. However, if your planted tank is looking a little bit sad or the plants look like they are in bad condition then test the Co2 level in your tank. You may need to supplement this with a Co2 tablet.

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What is a Co2 tablet?

Co2 tablets will dissolve in your home tank, giving your plants the valuable carbon dioxide that they so desire and require. This concentrated dose of Co2 will allow your plants to soak up a lot more of the important gas than they otherwise would from the air alone.

There are Co2 fertilizing systems for home aquariums, but often these can be complicated and costly. Co2 tablets remove the need for these by making the supplementation as easy as possible

Is a Co2 tablet effective in a planted tank?

Plants will only require Co2 during the light hours of the day. So, if you place a Co2 tablet in your home tank during the night, or even just before it gets dark, then you will see no improvement come the morning. This is because plants do not absorb Co2 in the dark.

In order for the tablet to be effective, you will need to make sure that there are enough hours of light left in the day for your plants to actively absorb enough of the gas from the tablet.

Typically, you will only need to add one tablet to your home aquarium every week (or 1 tablet for every 250 liters of water in your tank). Basically, the bigger your tank the more tablets of carbon dioxide you are going to need!

If your tank requires a lot of light (for example, for your algae) then you will need to ensure that your Co2 levels match this. Your plants can make use of most of the light available to them only if they have the other requirements to match it! So, the more light you have for your plants the more Co2 you are going to need (as a general rule). 

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Are Co2 tablets safe for fish?

Yes. Co2 tablets are perfectly safe for all fish, crustaceans, and plants that you can have in your tank. On top of this, they are also environmentally friendly. 

If you have other pets in your home the Co2-enriched water will also pose no threat to them.

Does Co2 reduce algae in a home aquarium?

If your plants are kept healthy (as well as the rest of your tank) then the likelihood that they will develop algae is indeed reduced. 

Algae will often occur in your home tank when there is an imbalance in the nutrients available. For example, if there is too much light and too little Co2 then it is very likely that algae will develop within your aquarium.

By ensuring that you strike the right balance between the nutrient levels and the lighting levels you can allow your plants to get the best of both worlds. They will grow and maintain good health and, at the same time, you can avoid having any algae in your tank. 

Can you add too much Co2 to a tank?

Yes, you can indeed add too much Co2 to your home aquarium. If your Co2 level rises beyond 30ppm then this can be dangerous and toxic for your fish. This is because your fish will then struggle to inhale the oxygen in your tank due to the overwhelming amount of Co2. Essentially, your poor fish may suffocate to death. 

If you find that your fish are swimming up to the surface to breathe regularly then this is a good sign that there is too much Co2 in your tank’s water. 

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To counter the amount of carbon dioxide in your tank you will need to aerate it. Simply placing an air pump in the corner will allow oxygen to be pumped into the tank’s water, giving your fish much-needed oxygen. This will then eventually bring the gas levels to a balance again. 


Having the correct amount of Co2 in your home aquarium is very important. It is a vital ingredient for your plants, contributing to their growth and overall health. It is used for both food and breathing, being turned into food through the process of photosynthesis.

If your Co2 levels are too low, for example, if they are out of balance with the lighting in your tank, then your plants may suffer as a result of this. 

By adding a Co2 tablet you can maintain good levels of gas in your tank, allowing you to keep a very healthy tank. Your plants will certainly thank you for doing so!