The 5 best bacteria for an aquarium

What are bacteria used for in aquariums?

In an aquarium, fish waste, leftover food, and plant debris release ammonia. Even in small amounts, this substance is dangerous for fish. Specialized bacteria convert it into nitrites, which are also toxic, and then into nitrates, which are much less harmful and are absorbed by plants and removed during water changes.

These bacteria live mainly in the filter, on sponges and media, and on the aquarium substrate. In a new aquarium, they are absent or few in number: it takes several weeks for them to establish naturally. Adding live bacteria helps speed up this process and restore balance after a disturbance.

When to add bacteria?

• When filling a new aquarium with water.
• After cleaning the filter or replacing its filter media.
• After a major water change.
• When adding new fish, which increases the waste load.
• After a water treatment that may have affected the filter bacteria.

Our selection of 5 bacteria for aquariums

We have selected these five products for their composition, ease of use, and clearly defined purpose. The information below comes from their product sheets.

1. Aquipond Aquarium Nitriboost

A liquid concentrate of nitrifying bacteria, designed to establish the nitrogen cycle more quickly and secure the ecosystem from the very first days. It is particularly suitable for starting up an aquarium and after operations that disturb the filter. Dosage: according to the label.

2. Bactocool Aquarium

Live bacteria for starting up a new aquarium or restoring biological balance, for example after cleaning the filter or adding fish. The product sheet states that a 100 ml bottle treats aquariums of up to 250 liters, and that it is preferable to pour the product into the filter. Shake well before use.

3. JBL Denitrol

A bacterial activator with enzymes, for freshwater and saltwater aquariums, also suitable for water turtles and shrimp. The product sheet gives a dosage of 10 ml per 20 liters when filling with new water, and 10 ml per 300 liters during a partial water change.

4. Sera Bio Nitrivec

A liquid filtration medium that combines cleaning bacteria with mineral volcanic rock. This provides a colonization surface for bacteria and helps bind turbidity. The product is presented as ideal after water changes. Dosage: according to the label.

5. Colombo Fresh Bacto

A biological activator specially designed for freshwater, based on live nitrifying bacteria, which promotes the decomposition of organic waste and speeds up the cycling of new aquariums. The 250 ml bottle is suitable for small to medium-sized aquariums. Dosage: according to the label.

How to choose between these products?

The five products pursue the same goal: to support the bacteria that convert ammonia and nitrites. The choice depends mainly on your situation:

• New aquarium: a concentrate of nitrifying bacteria such as Aquipond Aquarium Nitriboost or Bactocool, following the label.
• Saltwater aquarium or shrimp tank: JBL Denitrol, stated as compatible with these uses.
• Maintenance after water changes: Sera Bio Nitrivec, presented as ideal in this case.
• Small to medium freshwater aquarium: Colombo Fresh Bacto in 250 ml.

How to use bacteria properly

1. Condition the tap water if necessary before adding bacteria, so that they find favorable water.
2. Shake the bottle and measure the dose indicated on the label according to the actual volume of the aquarium.
3. Preferably pour near the filter or into the filter, where the bacteria will settle.
4. Leave the filter running continuously: bacteria need oxygenated water.
5. Test the water, especially nitrites, before gradually introducing the fish.

Bacteria, conditioners, activators: don't confuse them

In the aisle of products for aquarium water, several families coexist and are often confused:

• Live bacteria directly provide microorganisms capable of converting ammonia and nitrites. These are the products in our selection.
• Water conditioners prepare tap water to make it suitable for fish. They do not provide, in themselves, colonies of nitrifying bacteria, but they create good conditions for them.
• Activators or stimulants promote the development of already present bacteria, without necessarily bringing new ones.

These products are complementary: during a water change, a conditioner is often used for the new water, then bacteria if the filter has been cleaned. Read the label carefully to find out which family the product you have in hand belongs to.

A simple routine to keep bacteria active

Bacteria maintain themselves in a balanced aquarium. Your role is mainly not to disturb them:

• Change part of the water regularly rather than a lot of water at once.
• Alternate cleaning the filter and the substrate, a few days apart.
• Feed moderately: excess food increases ammonia.
• Keep a bottle of bacteria on hand to react after an incident.
• Record your water measurements in a notebook: a rise in nitrites is noticed more quickly when you know the usual values of your aquarium.

Mistakes that cancel out the effect of bacteria

• Cleaning the filter with tap water: chlorine and hot water destroy the colonies. Rinse sponges in aquarium water.
• Cleaning everything on the same day: filter, substrate, and a major water change at the same time removes most of the bacteria at once.
• Stopping the filter for several hours: bacteria lack oxygen.
• Overstocking the aquarium from the start: bacteria cannot keep up.
• Using an expired product or one stored in a warm place: live bacteria are sensitive to storage conditions.

If nitrites remain high despite everything, our article on nitrites that return in the aquarium helps you find the cause.

Frequently Asked Questions

What bacteria to put in an aquarium?

Live nitrifying bacteria, which convert ammonia and nitrites into nitrates. They settle mainly in the filter.

When to add bacteria to an aquarium?

When filling with water, after cleaning the filter, after a major water change, or when adding fish.

What dose of bacteria to use?

Follow the label of each product. For example, the Bactocool product sheet indicates 100 ml for an aquarium of up to 250 liters, and that of JBL Denitrol 10 ml for 20 liters when filling with water.

Can you add fish immediately after the bacteria?

Test the water first, especially nitrites, then introduce the fish gradually, in small groups.

Where to pour the bacteria?

Preferably in the filter or near its intake, where the bacteria will settle, with the filtration running.

Should you add bacteria at every water change?

This is not always necessary in a well-cycled aquarium. It is useful after a major water change or filter cleaning. Some products, such as Sera Bio Nitrivec, are presented as ideal after water changes.

Also read

• What are nitrites in an aquarium?
• Nitrites that return in the aquarium: find the cause
• How to start your aquarium and the practice of fishkeeping