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How often to Add Bacteria to Aquarium

More often than not, when you hear ‘bacteria’, you think ‘unhealthy’, ‘germs’, or ‘unsafe’. How often to add bacteria to Aquarium? Bacteria indeed have their fair share in being potentially dangerous to their host, by causing diseases and infections; however, one of the wonders of nature in aquascaping is how it makes use of what is considered ‘unsafe’.

As an aquascape hobbyist, your aquarium needs several bacteria to save the lives of your fish and plants, isn’t that interesting?

To make you see bacteria in the right context needed for this discourse, we will be referring to them as ‘beneficial bacteria’.

Your aquarium is a hub for chemical and biological activities that you need to keep up with to ensure that your fish and plants survive. That being said, your aquarium can not be left unchecked for even a day-especially a new aquarium. While beneficial grow and spread on their own, there are several ways to speed up their growth and how to incorporate them without affecting your water or its inhabitants.

In this article, you will come across the words ‘ammonia’, ‘nitrite’, and ‘nitrate’ frequently as they are the main actors that interact closely with the beneficial bacteria.


When your fish excrete waste, they decompose into ammonia, as is the case for dead plant decay, excess uneaten food, and decaying driftwood—they all become ammonia. Ammonia is highly toxic to fish; it burns fish gills and fins, causes swollen eyes, and breeds harmful algae. The smallest quantity of ammonia is more than lethal to your aquarium and should be curbed without delay.

The presence of beneficial bacteria is important in that these bacteria feed on the waste, maximally lowering the level of ammonia by converting it to less harmful nitrates.

While nitrates are not as dangerous as ammonia, they are still very toxic, and thus, the beneficial bacteria further break them down into nitrates, which are the least toxic if kept under control. For emphasis, you can NOT control ammonia or nitrites; while nitrates can be kept in check by frequent partial water changes which are important maintenance tasks in aquascaping.

Types of Beneficial Bacteria

For your aquarium to flourish, the need to be well informed of the biological and chemical rapport that goes on in there cannot be over-emphasized.

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That is why it is highly recommended that you be willing to carry out relevant research on any step you take in setting up and maintaining your aquarium.

The beneficial bacteria that are needed in your aquarium are of two types; they have classified accordingly to the specific work that they do.

Nitrosomonas Bacteria: These guys are responsible for breaking down ammonia into nitrates, so they are the first contact bacteria needed in your aquarium. 

Nitrobacter/Nitrospira Bacteria: They are the second category; and are responsible for the conversion of nitrites to nitrates.

How do these conversions take place? 

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Simple! The Nitrosomonas bacteria consume the ammonia and excrete nitrites, and then the Nitrobacter bacteria consume the nitrites and excrete nitrates.

So technically, these beneficial bacteria feed on toxic chemical compounds and turn them into less toxic ones that your fish need—everyone wins!

The totality of this process; from the establishment and growth of the beneficial bacteria to the work they do; which eventually leads to the production of nitrates, is known as the ‘nitrogen cycle’ or simply ‘cycling’.

This process usually takes a month or more, requiring close monitoring, patience, and dedication. To achieve the best results, we recommend that you prioritize the use of home test kits that help to check the ammonia, nitrite, and nitrate levels in your aquarium; as well as water PH.

Bear in mind that the survival of your fish depends on this. Spikes in the chemical compounds of your aquarium can pose a huge threat.

Adding Beneficial Bacteria to Aquarium

A tip to ensuring the successful addition of beneficial bacteria to your aquarium is to allow the cycle to complete before adding fish.

This means that you build up a solid base for the beneficial bacterial colonies to grow and cycle the tank properly.

This process demands a high level of patience but it is highly rewarding eventually; and the good news is that while you wait, there are a few ways to speed up the process!

OXYGEN: This is an important biological component for beneficial bacteria to thrive in your aquarium. You can incorporate oxygen into your water by pumping air into it or by increasing your water temperature.

The second step is quite tricky; you don’t want to wind up escalating potential danger by spiking your water chemistry. It is correct that warm water provides an ideal environment for beneficial bacteria to reproduce, but it is imperative to note that it has to be carried out with utmost caution.

As a guide, make sure the water temperature is kept around a sweet 85°F. Also, do not have fish in your aquarium during the process of increasing water temperature.

LIGHTING: While your aquarium must be sufficiently supplied with natural and artificial lighting, you may want to tone it down a bit during the cycling process. Beneficial bacteria; especially Nitrosomonas, grow faster in the absence of light.

Until the cycle is complete, cut down on those lights and avoid exposing your aquarium to sunlight as it will both retard the growth of the beneficial bacteria and breed algae.

FILTER MEDIA: Filter media is a part of your water filter that directly affects the quality of water in your aquarium. In speeding up the ‘cycling’ of your aquarium, let your filter run! In the process of cleaning your aquarium, do NOT attempt to rinse your filter media with any other water but tank water. Using chlorinated water will be counterproductive, and reverse the entire cycle.

This prep process makes your aquarium a conducive environment for the growth of beneficial bacteria. Don’t be in such a hurry to add fish, ensure your aquarium is set to accommodate your fish and plants first. - For all your creative needs!

Already have fish in your aquarium?

Don’t fret, you can cycle your aquarium with fish in it. The trick is to feed your fish within small rations for a while and then increase the rations after two to three weeks.

The reduction will reduce the rate at which your fish excrete waste; giving the bacteria plenty of time to gain ground and spread all over your aquarium.

You’ll know that the cycling process is complete once your water is free from ammonia and nitrate even after feeding your fish their regular food ration. Ensure your home test kit is original and tested to give you accurate results.

The actual addition of bacteria to your aquarium may be categorized into two; manual and biological. The manual process is the direct addition of nitrifying bacteria to your aquarium through a process called seeding.

This can be done by purchasing original, organic beneficial bacteria starters and seeding them in your aquarium. The beneficial bacterial starters usually come in bottles and are sold online and in pet shops.

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Once again, ascertain the authenticity of the supplier and the product before purchase.

Bacteria can be developed biologically or indirectly through a process known as plant cycling. If you are not big on having a near-empty tank just to allow for bacteria to grow, you can add live plants to your aquarium.

These plants consume waste just as fast as Nitrosomonas bacteria convert them to harmless bacteria. Simply grow live plants in your aquarium and nurture them with appropriate fertilizers and sunlight, and watch them rid your water of ammonia and nitrites by transforming them into new roots and leaves.

Plant cycling serves two purposes simultaneously: the biological transformation of your aquarium and visual appeal!

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How often to add Beneficial Bacteria to Aquascape Aquarium

To the crux of the matter, the frequency of adding bacteria to your aquarium is largely dependent on several factors.

These include. However, a common ground for these factors is that beneficial bacteria must be part of your aquarium set up from the beginning.

Do NOT skip this step! The life span of your aquarium and its inhabitants depend on how often you add bacteria to your aquarium.

We shall examine the different durations of adding bacteria to your aquarium and compare them; to determine how often you must do so:

Daily Addition of Bacteria

We do NOT recommend that you add bacteria to your aquarium daily. 

Not only will this expose the fish to harm, but you will also wind up reversing the cycle every time you add new bacteria. It had been extensively discussed in this article that the cycling process takes a couple of weeks to complete.

Imagine adding new batches of bacteria to the ones in the aquarium that have barely begun to gain base. You will end up with an aquarium overridden with undeveloped bacteria; or worse, an algae invasion.

Weekly Addition of Bacteria

Bacteria is typically self-sustaining. This means that in an ideal environment, you need to add only a little bacteria to your aquarium at a time; then they multiply.

In other words, you may not need to add new bacteria every single week as long as you added enough in the beginning. However, weekly or bi-weekly maintenance tasks like water changing may necessitate adding bacteria more frequently.

This is because a quantity of bacteria is cleared out when you change your water, and you will need to supplement the residual bacteria in your aquarium with a new batch to maintain balance in your water chemistry.

Monthly Addition of Bacteria

As a result of water changes or other possible activities that come up in your aquarium, you will have to add bacteria to your aquarium at least twice or thrice in a month.

This makes it the most realistic and practical frequency of incorporating beneficial bacteria into your aquarium, instead of the aforementioned two.

Helpful tips in adding Bacteria to your Aquarium

  • Study and understand the nature and dynamics of your aquarium to be well-equipped will how often to add bacteria to it.
  • Purchase original home testing kits needed to measure water levels.
  • Pay close attention to; and monitor ammonia, nitrite, and nitrate levels in your aquarium; as well as water PH level. If ammonia and nitrite levels are in very low or zero PPM, you have little need for new bacteria incorporation.
  • Don’t overfeed your fish, too much uneaten food in the water will ‘distract’ the bacteria from other functions in the aquarium.
  • Don’t rinse out your water filter media, the bacteria growing it is useful to your aquarium.


Owning an aquarium is a hobby that needs devotion and this is evident in many ways; including the need to regularly track the activities of chemical and biological components in your water.

Beneficial bacteria are irreplaceable in your aquarium; adding them to your aquarium in the right quantity, at the right time will be great for your aquarium!