Bacterial Bloom Not Going Away [Top 5 Reasons Solved!]

Bacterial bloom might be good for your fish tank because they promote healthy aquariums.

But having this bacterial bloom can be annoying. But of course, there’s a reason why it stays for so long in the aquarium. 

Why is bacterial bloom not going away?

Bacterial bloom is primarily caused by a sudden surplus of nutrients in the aquarium. They usually go away within 10 days, naturally.

But if not, there’s likely an external factor sustaining them. Overfeeding, overcleaning, and irregular or large water changes might cause them to stay longer. 

However, this is merely a summary of the entire issue. If you’re interested in details, we’ve written the perfect article for you!

Let’s begin reading!

What Is Bacterial Bloom?

Bacterial bloom is the sudden increase in bacterial colonies in the aquarium.

This is caused by an increase in nutrients or ammonium production.

The bacterial colonies try to restore equilibrium by multiplying themselves. 

Bacterial bloom is most common in new fish tanks. It’s also common in tanks with excessive feeding or unremoved dead fish and plants. An increase in potassium and nitrates can also cause bacterial blooms.

Wondering: what are the symptoms of bacterial bloom?

The bacterial colonies grow so fast that they are visible to human eyes. This causes the water to become milky and blurry in appearance. This is the only symptom of a blooming bacterial colony.

What Are The Effects of Bacterial Bloom?

The effects of bacterial bloom can be discussed based on their types. Bacteria are of two types:


These are called beneficial bacteria. These bacterial blooms are not harmful to the fishes inside the aquarium. 

They feed on inorganic matter, like ammonia, light, etc. When these bacterias grow, they starve the cloud-causing heterotrophic bacteria away. 


They are known as cloud-causing bacteria. They feed on organic matter, like feces, dead fish, etc. 

These require a large amount of oxygen. In their aerobic stage, they can cause huge oxygen drainage.

These are the types of bacteria that we don’t want in our tanks in excess.

They can double within 15 minutes. They reproduce so fast that they can be seen with bare eyes as milky clouds in a tank.

What Are The Reasons Behind Bacterial Bloom Not Going Away?

So, we’re all clear about bacterial bloom now. But what’s the reason behind its long stay?

Well, we’ve some reasons here-

Reason 1: Overfeeding

The most common reason behind bacterial bloom is overfeeding your fish.

Overfeeding your fish causes an increase in ammonia in the tank, which is produced from a large amount of byproduct from fish due to excessive eating. 

By the way, overfeeding can also be the cause behind corals like Acan corals dying. So yeah, you have to be careful with the feeding process.

Bacterial colonies tend to increase to cope up with excessive ammonia in the tank. 

Solution: Feed Only When Required

Keep your food provision in check. Fish can consume their food within 2 minutes of serving. 

If there is excess food left after two minutes, that’s a sign of overfeeding. Adjust your feeding schedule based on this, and the bloom will disappear.

Reason 2: Dirty Filter

Water filters are supposed to pump water in a specific volume. If this filter is clogged by dirt, residue, or algae slime, it won’t function properly. This is why the bacterial bloom stays instead of fading.


Clean your filter and get rid of any sort of clumps or slime. This will help the filter to function as intended. 

This can clear the bacterial bloom overnight. You can opt for replacing your filter if the current one is too old.

Reason 3: New Fish Cycle

You might introduce new groups of fish into an aquarium. Unfortunately, this can cause ammonia and nitrite levels to spike. 

Bacteria colonies multiply themselves to cope with this spike. Thus, we can observe a bacterial bloom.

Solution: Be Patient While Introducing Fish

As an immediate solution, you must clear out the extra nitrite and ammonia levels. After that, you need to focus on prevention.

The smartest way to solve this is by introducing fish gradually into the new tank. In this way, you can prevent ammonia and nitrite spikes, which can be fatal for the fish.

You should always check if fishes are compatible with previous fishes. If not, don’t worry! Some fish species, like clownfish, can also live alone

Reason 4: Overcleaning

Cleaning too frequently causes bacterial colonies to weaken. So, they fill the gap by rapidly reproducing. 

Overcleaning mostly causes the heterotrophic bacteria to continue this cycle. As a result, we observe a prolonged bacterial bloom.

Solution: Clean Tank When Needed

Do not clean your tank to eliminate the bacterial bloom because that can be counterproductive. Instead, cleaning your tank once every two weeks should suffice.

Reason 5: Unnoticed Debris

Another reason could be the clustering of unnoticed debris in the tank. Heterotrophic Bacteria feed on debris. The debris includes dead fish, dead plants, feces, etc. 

As long as these remain in the aquarium, bacteria will bloom. Furthermore, dirty water is also a reason behind anemones deflating.

Solution: Clean Out The Debris

The best solution is to vacuum the gravel. This will strip the gravel of the aquarium of any sort of waste. 

The waste includes dead scales, uneaten food, dead bits of fish, and plants. This keeps the gravel color bright and the fish tank healthy. 


Question: How long does it take for a bacterial bloom to go away naturally?

Answer: It takes 5 to 12 days to go away naturally. This is unless any external factors cause it to stay longer.

Question: What is the mechanism of a bacterial bloom?

Answer: Heterotrophic Bacteria multiply very fast compared to beneficial autotrophic bacteria. Beneficial bacteria starve away the cloud-causing bacteria.

But it needs time to catch up to the heterotrophic population. So, bacterial bloom persists for a few days.

Question: Do shutdowns of filtration systems cause bacterial bloom?

Answer: Yes, long shutdowns do cause a bacterial bloom. Ideally, filtration should always be kept on. 


So, that’s all we have on ‘bacterial bloom not going away. We hope we’ve been able to help you solve your problem.