5 Causes of Bacterial Bloom (How Long It Lasts + 5 Ways To Avoid It)

Aquarium with bacterial bloom

Noticing a bacterial bloom in your aquarium can be frustrating.

It makes your fish tank look ugly and ruins its aesthetics.


How Long Does a Bacterial Bloom Lasts?

A bacterial bloom can go away on its own in 7 to 10 days from a new aquarium. However, it can take several weeks or even a month to go away from established tanks. It depends on the size of the tank and the extent of the bacterial bloom.

Let’s now learn more about the various reasons that cause bacterial bloom and effective ways to avoid it.

But first, let’s understand how to identify a bacterial bloom.

Signs of Bacterial Bloom

Identifying bacterial bloom in aquariums is easy. Bacteria increase rapidly, and collectively they are visible to the naked eye.

The most common sign of bacterial bloom is that the tank water turns cloudy or milky.

You will even notice an increase in the ammonia levels of the tank water, which makes the fish lethargic.

If the bacteria increase, the tank water will be so unclear that you won’t be able to spot your fish and plants clearly.

If you notice any signs of bacterial bloom, it’s vital to take action immediately.

5 Causes of Bacterial Bloom

Bacterial bloom is a condition wherein there is a sudden rise in the number of bacteria.

Many different factors cause a bacterial bloom. Some of the common causes are listed below.

1. New Tank Setup

Bacterial bloom is typical in newly set up tanks.

It isn’t a condition to worry about as it’s normal and goes away on its own once the tank is established.

Low chlorine level causes a bacterial bloom in new tanks as it helps the bacteria to grow in colonies.

Introducing more fish in a new tank is another reason that causes bacterial bloom.

The higher the number of fish, the more the fish excreta.

This increases the chances of bacterial growth.

Also, fish, plants, live rocks, and other equipment contain microorganisms within them.

So when you introduce them in the tank, the microorganisms contribute to the bacterial bloom.

2. Overfeeding

Overfeeding is one of the primary reasons for bacterial bloom in aquariums.

Fish food contains vitamins, phosphates, and other nutrients that encourage bacterial bloom.

Excessive feeding results in leftover food, which gets decomposed by bacteria if it’s not removed immediately.

This decomposition process releases ammonia into the water, leading to bacterial bloom.

Overfeeding also results in the production of excess waste by the fish.

If this waste isn’t filtered out from the tank, it accumulates organic matter in the tank water.

The accumulated organic matter encourages bacterial growth.

3. Increase in Nutrients

Decaying fish and plant material decompose in the tank water if they aren’t removed immediately.

Due to this decaying process, several nutrients get released into the tank water.

This results in an increase in the nutrient levels of the tank water.

The excess nutrients promote bacterial growth and result in bacterial bloom.

Nutrients such as phosphates and nitrates are essential for fish, but too much of them encourages bacterial growth.

4. Poor Filtration

A poor filter allows unfiltered particles to stay in the tank water, which contributes to bacterial growth.

Inadequate filtration systems result in a higher concentration of ammonia and an increased level of nutrients in the tank water.

This leads to increased bacterial growth, thereby promoting bacterial bloom.

5. Unmaintained Tank

Tank maintenance is key to keeping your fish healthy.

A well-maintained tank ensures proper water circulation, oxygenation, waste removal, etc.

If these processes aren’t working correctly, then the chances of bacterial bloom increase.

Bacteria thrive and multiply rapidly when the water quality is poor. This leads to the formation of large colonies of bacteria.

In this case, the water turns milky and becomes opaque.

Lastly, if the substrate isn’t cleaned regularly, a large quantity of fish and plant waste accumulates at the aquarium’s base.

This causes all kinds of bacteria to breed in the water, resulting in bacterial bloom.

5 Ways to Avoid Bacterial Bloom

A bacterial bloom usually goes away in a few days from newly set-up tanks.

However, in established tanks, you need to find a way to get rid of it.

However, prevention is better than cure.

So you can always take the necessary steps to prevent a bacterial bloom in the first place.

Given below are some ways to avoid a bacterial bloom in your aquarium.

1. Avoid Overfeeding

Man feeding fish in an aquarium

Avoiding overfeeding your fish goes a long way in preventing a bacterial bloom.

Overfeeding leads to uneaten food, which settles at the tank’s bottom or dissolve in the water.

If the leftover food isn’t removed, it acts as a food source for the bacteria and maximizes their growth.

So you must feed your fish as much as they can consume in a couple of minutes.

Ensure that your fish get the required nutrition without overfeeding.

2. Perform Regular Water Changes

Changing the tank water regularly helps to avoid a bacterial bloom.

Expert aquarists have rarely experienced bacterial bloom with regular water changes.

Even if the bacteria occur, the colonies won’t be large enough to cover the entire aquarium.

Partial water changes help remove the additional nutrients from the tank water.

So the bacteria don’t multiply due to insufficient nutrients in the water.

You can regularly perform a partial water change of 20% to 30% to curb bacterial bloom.

3. Perform Regular Maintenance

Keeping a fish tank clean prevents the accumulation of debris and other unwanted materials in it.

This reduces the possibility of a bacterial bloom.

The most effective way to avoid a bacterial bloom is to remove the excess organic materials from the tank water that cause the bacterial bloom.

So decaying fish and plants should be removed immediately.

They decompose in the water, releasing nutrients that stimulate bacterial growth.

Similarly, uneaten fish food, fish waste, debris, and detritus must also be cleaned regularly to curb bacterial bloom.

4. Check the Aquarium Filter Regularly

An aquarium filter plays a vital role in maintaining water quality.

It helps remove unwanted materials from the water, thus keeping it clean.

If the filter is worn out or not working correctly, it increases the ammonia levels of the water since the waste doesn’t get filtered out.

This provides excess nutrients to the bacteria that they consume and grow.

So filter media should be cleaned and replaced regularly to prevent bacterial blooms.

Regular cleaning of the filters removes debris and decaying organisms from the filter media.

It also prevents clogging of the filter and improves its efficiency.

5. Add Beneficial Bacteria

Beneficial bacteria play a crucial role in curbing bacterial bloom.

They decrease the nitrogen cycle rate, which promotes bacterial bloom.

Several products are already available in the market to introduce beneficial bacteria in an aquarium, which helps to reduce bacterial blooms.

What Bacteria Commonly Cause Bacterial Bloom?

An excess of heterotrophic bacteria causes bacterial bloom in aquariums.

These bacteria are present in small numbers in aquariums and are healthy as they help break down fish waste.

However, heterotrophic bacteria are problematic when they start multiplying rapidly. This leads to bacterial bloom in aquariums.

These bacteria feed on organic materials dissolved in the tank water.

They are very flexible and overgrow rapidly if not controlled on time.

Heterotrophic bacteria usually form colonies on the aquarium substrate or gravel or sometimes in the water column itself.

Is Bacterial Bloom Harmful to Fish?

A bacterial bloom harms the fish if it’s not controlled quickly.

Most bacteria are aerobic. They need oxygen to survive and flourish.

Hence, the oxygen level in the tank decreases if bacterial colonies are formed.

The tank inhabitants suffer if the oxygen level remains low for a considerable time.

However, this issue can be resolved with an adequate aeration system.

A bacterial bloom also causes ammonia levels to spike. This is also be very harmful to the fish.

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