CO2 in a Shrimp Tank

Today I would like to touch a very delicate topic – CO₂ in a shrimp tank. The point is that a lot of aquarists have had to settle with the knowledge that carbon dioxide or CO₂ is extremely unsafe for shrimp. Is it so or not?

What if I tell you, that CO₂ and shrimp can do just fine if you are running it properly at a safe level! If you do everything right, it will not cause problems for your shrimp, fish, and snails.

Of course, as expected, there are many shrimp keepers who claim that their shrimp tanks have been better off without any carbon dioxide. At the same time, the opposing camp has always claimed otherwise. This has left the world of aquatic enthusiasts in complete chaos. As a result beginner aquarists have lots of questions such as:

1. How does CO₂ affect Shrimp?
2. Is there a safe level of CO₂ in a shrimp tank?
3. Is CO2 useful for planted tanks with shrimp?
4. Do I need CO₂ in small tanks?
5. What is the correlation between CO_2, pH, KH, and shrimp?
6. CO₂ and overdosing. How can I save shrimp?

These and some other questions will be discussed in the course of this post. Let’s start with the most important ones.

How CO2 Effects Shrimp

Shrimp are more susceptible to a rise in environmental CO₂ concentration than terrestrial animals, because of the lower CO₂ partial pressures of their body fluids. Ventilation is governed by O₂ stimuli because of the low O₂ concentrations in water.

Note: O₂ concentration in water is ∼1/30 of that in air.

This situation necessarily results in hyperventilation of shrimp in terms of CO₂ excretion, because CO₂ solubility in water far exceeds O₂ solubility. Thus elevations of CO₂ in water will easily reverse the normal outward diffusion of CO₂ from the shrimp body. Basically, high CO2 in the water kills shrimp because they are not able to expel the CO2 in their system.

Sighs of CO2 overdosing – suffocation:

1. Staggering swimming behavior.
2. Shrimp stop moving.
3. When they lay on their side.

Is there a safe level of CO2 in Shrimp Tank?

I have read lots of articles, and discussions on forums (English, German, and Russian) about CO₂ and shrimp. The most interesting part here is that people usually do not operate with specific numbers. Why? Because it depends on your water parameters and how many plants you have in the tank.

However, if you are interested at least in average results, I can tell you that. The optimal CO₂ concentration in an average planted tank is 15 – 20 mg/l. The dangerous limit for shrimp is considered 30 mg/l.

First of all, I need to start off by saying that having between 10 and 30 ppm can be considered a lot for aquatic water bodies. Especially if you compare it with the regular amount that is supplied by non-CO₂ injected shrimp tanks with RO/DI water. You only have about 2 to 3 ppm supplied by such tanks, which makes it to be in equilibrium with atmospheric oxygen, given gas laws.

However, natural water on its own is composed of carbon dioxide (CO₂) at different levels. It can normally contain even up to 10 ppm, which is provided by organic matter that decays in such water column. While some ground waters may easily exceed that concentration.

According to the study on the toxicity effects of CO₂ in juvenile (1.76 ± 0.36 g) white shrimp (Litopenaeus vannamei). Biologists exposed shrimp for 96 hours to one of six concentrations of dissolved CO2 (14.5, 23.8, 59.0, 88.0, 115.0, and 175.0 mg/L).

The LC50 values with 95% confidence limits at:

• 24 h – 130.05 (104.2–162.1) mg/L of CO₂.
• 48 h – 77.2 (73.8–80.02) mg/L of CO₂.
• 72 h – 69.65 (65.47–74.32) mg/L of CO₂.
• 96 h – 59.12 (53.08–66.07) mg/L of CO₂.

The highest concentration that did not induce significantly higher mortality was 23.8 mg/L of CO2. Although that experiment was not on dwarf shrimp species, it still gives us some real data.

In addition, aquascaping pioneer Takashi Amano constantly thought of an effective way to supply CO2 in water.  Proper lighting and CO₂ injection are essential for growing healthy aquatic plants and creating a beautiful aquatic plant layout. What is more interesting for us is that he used shrimp in most of his aquascapes!

This is another prove that CO2 and shrimp can “coexist” if you do everything right.

Note: Caridina multidentata (Amano shrimp) was introduced to the aquarium hobby by Takashi Amano in the early 1980s (It is also from him where they got the name since 2006).

Is CO2 Useful for Planted Tanks with Shrimp?

In general, when there is an inadequate amount of СO2 in a planted tank, plants are bound to be affected by experiencing stunted growth, which can potentially affect your shrimp. Let me elaborate a little bit here.

Plants play a very important role in a shrimp tank. They provide additional chemical filtration, aeration, hiding places, surface area, etc.

Adding additional CO2 around plants is similar to adding additional nitrogen to the soil. They start thriving. Therefore, the health of plants directly affects our shrimp. Shrimp do not need CO₂, they need healthy plants.

Do I need CO₂ in Small Tanks?

In most cases, you do not need CO₂ in small tanks. CO₂ systems will be ideal for people who grow plants that require intense light and high nutrient concentration. If you have only a few plants in your shrimp tank, injection of CO2 can do more harm than good.

Actually, this is a very common mistake. Beginner aquarists usually think that adding CO₂ will be just enough to get a beautiful planted tank. This is WRONG!

There should always be a balance. Without the right amount of CO2, light, and fertilizers, your tank will suffer from algae outbreaks. For example, if you increase the level of CO₂ but do not change the light and fertilization, your plants will not be able to use more CO₂. Because plants need light to perform photosynthesis. For better growth, they will also need additional nutrition (fertilization).

What will happen with the excess of CO₂? The fluctuation of CO₂ will cause algae growth. What will happen with the excess of the light? Algae will use it.

Note: Another problem is that many fertilizers contain copper. Read more about it in my article “How Copper Affects Dwarf Shrimp”.

Of course, algae in the shrimp tank is not a big problem. Shrimp will eat it. Although, it also depends on the type of algae. You can read my article about “Types of Algae. Best Algae Eating Team”. The point is that if you are new to this hobby, do not overcomplicate your life until you know exactly what you are doing.

Note: In the wild, according to studies, the most common food is detritus, which was found in 93% in shrimp guts (Algae are in the second place – 65%).
Tip: There are many plants however which will still flourish without CO₂ and/or any fertilizer. Actually, these plants will be ideal for a shrimp tank. You can read my article “Top 5 Plants for Your Shrimp Tank”.

What is the Correlation between CO_2, pH, KH, and Shrimps?

CO_2, and pH

There is a direct correlation between CO₂ and water parameters (pH, KH).

The measure which indicates whether water is acidic or basic is known as pH. More precisely, pH indicates the hydrogen ion concentration in water and is defined as the negative logarithm of the molar hydrogen ion concentration (-log [H+]).

You can read more about it in detail in my article “Water Parameters: Everything about pH in Shrimp Tank”.

In planted tanks, carbon dioxide normally builds up in the night when it is getting dark. Therefore, pH varies throughout the day due to respiration (shrimp, fish, snails, and even bacteria) and photosynthesis.

At night, dissolved oxygen concentrations decline as photosynthesis stops, and all plants and animals in the tank consume oxygen. In heavily stocked tanks (especially in community tanks), carbon dioxide concentrations can become high as a result of respiration. The free CO₂, released during respiration reacts with water, producing carbonic acid (H2CO3) and pH is lowered.

During the day, CO₂ is removed by plants. So, the pH level will increase throughout the day.

CO_2, pH, and KH

Carbonate Hardness (KH) is measured by the amount of acid (hydrogen ion) water can absorb (buffer) before achieving a designated pH. In other words, the ability of a solution to resist a pH change with the addition of an acid.

You can read more about it in detail in my article “Water Parameters: Everything about KH in Shrimp Tank”.

So, KH prevents acids from causing sudden drops in our pH. It means that higher amounts of CO2 (i.e., carbonic acid) are required to lower pH because there is more base available to neutralize or buffer the acid. The pH of well-buffered water normally does not fluctuate much. In waters with low alkalinity, pH can reach dangerously low or dangerously high levels. Which will be extremely dangerous for your shrimp (fish or snails).

Therefore, if your KH is high it will not let pH drop after CO₂ injection. The problem is that high KH will make your water too hard, and it will significantly increase your initial pH. As a result, if you want to get the desired pH level it will be necessary to exceed the safe level of CO₂ concentration. That will kill every shrimp, fish or snail in your tank.

In addition, it is very important to know that shrimp are not a fan of sudden changes in pH. Although they can tolerate gradual changes, sudden swings (within an extremely short period of time) can shock and kill them as well.

If the changes within the shrimp tank are still within the shrimp pH range, then the CO₂ amount may not make much difference as it will be able to accommodate the changes in pH. So while pH swing is very important because of the changes caused by injected CO₂, it is also important that aquarists draw the line between changes in pH and having extreme pH values at each in point in time. 

Note: Sometimes you can see graphics where you can determine the CO₂ level in a tank from KH and pH. Well, DO NOT trust them. There is no way you can determine the CO₂ level in a tank from KH and pH. In 99% you will get an overdose.

CO2 and overdosing. Saving Shrimp. H2O2

If you see that your shrimp has become lethargic, stopped moving and lay on their side. It is a sure sign of CO₂ overdose and you do not have much time to save them. What should you do when you see that there was CO₂ overdosing and your shrimp are not moving? How can you eliminate hypoxia (lack of oxygen)?

You can use H2O2 (hydrogen peroxide). Hydrogen peroxide is a very powerful oxidizer. It decomposes into harmless water and oxygen very fast.

However, you can add 3% hydrogen peroxide directly to your tank but only by following some instructions.
Warning: DO NOT overdose H2O2. Check and double-check your calculations. Overdosing can kill your shrimp as well.

1. Turn off your filter.
2. Use 3% Hydrogen peroxide at 1 – 1.5 ml per gallon or per 4.5 liters.
3. Evenly spread H2O2 across the surface of the aquarium.
4. Gently stir the water to spread it.
5. Wait for 15 minutes.
6. Turn your filters back on.
7. The same week do a water change and add your favorite bacterial supplement back to the tank.

After that, there will be enough oxygen for your shrimp and they will start returning to the world of the living. If there is no effect after 15 minutes of exposure, it was simply too late.

Note: H2O2 can be used as an antiseptic and an agent for controlling external parasites. You can learn more about it in my articles “Hydra in a Shrimp Tank. Treatment” and “Ellobiopsidae or Cladogonium ogishimae. Green Fungus in Shrimp Tank”.

In Conclusion

Shrimp do not benefit directly from CO₂, they benefit from the plants. Adding additional CO₂ around plants is similar to adding additional nitrogen to the soil – it gives plants a boost to grow more rapidly.

However, if you want to use CO₂ in your shrimp tank, there are rules you need to follow. There should always be a balance of light, CO₂, fertilizers, and water parameters. Otherwise, instead of a beautiful planted tank, you will get algae outbreaks. In the worst-case scenario, you will kill everything in the tank.

Personally, if you have a small tank with a few plants I do not see any reason to use CO₂. There are too many things you will have to control. Keep in mind that shrimp do to like changes.

Related articles:

CO2 in a Planted Tank Guide