Introduction: CO2 for Your Aquarium Made by Mushrooms

A simple and easy way to produce CO2 for your aquarium using Oyster mushrooms.

Step 1: An Easy Way to Ad CO2 to Your Aqaurium Made by Mushrooms

Most people know CO2 is a key component to let plants in your aquarium grow better, and although there are many products to buy that produce CO2, I have invented a way to do the same, but cheaper and in a more sustainable manner.

I have worked many years in sales selling aquarium products, but I always struggled to make my plants grow well without using a lot of extra's. I tried many different ways to add CO2, using yeast (, CO2 tanks an even a fully automated system with a PH sensor and computer.

But most of it failed because of complications with the electronics or simply because of my own mistakes and forgetting to add new bottles with sugar and yeast.

Than I found an interesting article about farming Oyster mushrooms and the simple fact that when they develop they use, like we do, O2 and exhale CO2.

This article on Instructables explains a lot on farming Oyster mushrooms

I think we can use many different kinds of mushrooms but I use the Oyster Mushroom because these are a modified mushroom that do not produce spores. Spores can be dangerous for your health.

This article is not about producing Oyster mushrooms but it is a nice extra that the mushrooms will grow while they produce the CO2 which leaves you with a nice meal after 2 or 3 months.

Step 2: How It Works

First you need an Oyster mushroom “grow kit", a small bucket (3,5 liter bucket for 160 liter aquarium) with an airtight lid, a simple aquarium air pump with an air stone or a diffusor and 2 simple air nipples to connect the air hose to the aquarium.

There are two ways to do this:

Use an air pump to push the fresh air trough the bucket filled with spores and grow medium to the aquarium or use a diffusor.

The simplest way is to use an air pump. Connect the hoses to the bucket and push fresh air trough the bucket to the aquarium. The mixed air and CO2 is pumped into the aquarium using an air stone.

The second way is to use a diffusor in combination with the main filter pump. Use the outflow from your pump and connect the diffusor and the end. Fresh air is now sucked in trough the bucket and will be mixed with CO2. Not all diffusors will work the same way because the outflow needs some pressure to work properly. The one in the picture is from Eheim en will work with a very low outflow.

in order to let the mushrooms grow (depending on your grow kit) you need to add boiling water to the bucket. Close the lid after you add boiling water and let it cool down. Be carefull and mix the spores trough the growth medium with a clean spoon. This is where things can go wrong. Many wrong fungi spores will be present in most homes and they can get into the growth medium. This will destroy the development of the mushrooms. So be sure to do this as clean as you can. Wash all of your equipment before letting them make contact with the growth medium and or mushrooms to prevent contamination.

Within a day the spores will start to develop and produce CO2.

Step 3: Harvest the Mushrooms

Put the set in a dark place, the set will produce CO2 for one to three months depending on the temperature of your house. After one or two months little knobs will appear and they can develop into full mushrooms if you take them out of the dark and into the light. place them in a moist environment.

If you let them in the dark, they will stop growing but will keep producing CO2 for a while longer. after 2.5 month, check growth of the knobs. When they stop growing you need to restart the hole set with a fresh growth set.

Step 4: Advantages and Disadvantages

I like this way of adding CO2 to the aquarium because it is easy and environmentally friendly. You can use many different kinds of growth mediums but it will work best with straw or used coffee grounds. Make sure you sterilize everything to prevent the growth of the wrong fungi.

Most grow kits will have a growth medium delivered with it, follow their instructions to start the kit.

There is very little risk of adding too much CO2 using mushrooms. which can kill your fish. This can happen if you are using very soft water (like rain water). Always check your GH and KH, if they are above 5 you should be save. Most problems with overdosing Co2 will happen when the lights in your aquarium are out. This is the moment when your water plants start producing CO2 instead of O2.

A good circulation from the pump and or the air pump will stop the build-up of dangerous CO2 levels. If you have any doubts block the CO2 flow from the bucket with mushrooms to your aquarium, but make sure the air still flows trough the bucket, the mushrooms need air to breath.

It is wise to check the levels of CO2 with a permanent CO2 indicator this will tell you if there are dangerous CO2 levels present.

Once the spores develop into mushrooms you have at least 6 weeks of CO2 production to make your plants grow better. The remaining´s of the growth medium can be used as a fertilizer for your garden.

Check the air flow after a while because the mushrooms will block the air hose if not stopped in time.

I use a 3,5 liter bucket on a 160 liter aquarium, this seems to produce enough CO2. I just started a 40 liter aquarium with a glass jar filled with spores and growth medium and this seems to work fine too.

The photos from my aquarium shows the changes since I started to ad CO2 in November 2018. I did not add any additional nutrients and only changed 50% of water every 4 weeks.

If you live in the Netherlands you can order a full set and starter set here: