How Do You Treat a Bacterial Bloom?-Easy Guide

You have put in countless hours selecting the perfect fish, arranging the best plants, and ensuring that the water is just right for your aquarium. It seems that you have done everything right, but one day you wake up and the water is filled with a cloud of nasty bacteria. 

How do you treat a bacterial bloom? If you have an established aquarium, start by taking water from the substrate. Siphon gravel from the bottom of your aquarium and perform about a 25 percent water change. Once out, add new water that has been treated. This will remove built-up debris and waste and help keep the new water clear. 

It is so frustrating to find your aquarium and a cloudy state full of bacteria that is simply unwelcomed. This is a problem that many tank owners will face, no matter how experienced they may be. Don’t stress though, there are plenty of ways to get rid of this unsightly matter. Continue reading to understand what exactly a bacterial bloom is, how long they last, and the easiest ways to prevent them from happening in your aquarium.

What is a Bacterial Bloom?

We all know there is such a thing as good bacteria and bad bacteria. For your fish tank, this holds true just as well. Within an aquarium, there are types of heterotrophic bacteria that are naturally occurring. 

These are very versatile and can live in lots of different environments whether the oxygen is high or it is low. For your tank, this is great because they are able to do their job with little interference from you. 

These bacteria help to break down the waste in your aquarium. You may not think that much waste exists within it, but when you account for the waste your fish produce, and all the leftover food that settles at the bottom of the tank, there is more than enough waste for this bacteria to chomp down on. 

Because of this existing waste, you need a certain amount of this bacteria in order to rid your tank of its garbage. Now, when a bacteria bloom occurs these bacteria grow so quickly that they take on a bigger role in your aquarium than needed. In essence, they become too much of a good thing. 

When the bacteria overpower your tank and start to make the water cloudy, this is created through a large consumption of oxygen in the water by the bacteria itself. Increased ammonia levels can also team up with bacterial blooms so be sure to routinely check your waters levels.

How Long Does a Bacterial Bloom Last? 

This can be a bit of a tricky question. You see that your tank is lacking in clarity and it continues for a few days. You may try a few tips and tricks, but the problem seems to only get worse and persist on. 

What is so rotten about a bacterial bloom is that you don’t want to rid your tank of all bacteria present. If you do this, the issue will only intensify and you will be left with more work than you started with. There is a delicate balance needed to find a resolution.

Bacterial Bloom in New Aquariums 

First, let’s address those who have brand new aquariums. For an aquarium, there are all sorts of organisms that exist on the fish you put into your tank, the live plants that will be placed within it, and even on rocks that go inside. 

When you put all of these components together in water that also has its own microorganisms within it, a bit of kickback will certainly occur. After all, everything involved in the new tank is trying to get acclimated and this can take time.

Because of this “getting to know each other phase” the water in your tank can get a bit cloudy due to a bacterial bloom. Your first instinct may be to immediately change the water and begin cleaning the inside of the tank, but this will only make matters worse. 

Before scrubbing down the walls, give your tank a little time to adjust. The bacteria need a few days to level itself out and settle. This should take around 2-4 days and your tank should begin to clear up. 

Bacterial Bloom in Established Aquariums

If you have an established aquarium, then a new environment settling down is clearly not your issue. At this point, you understand what a bacterial bloom is, but it can still be a bit of a conundrum to solve. 

For older established aquariums, you need to first get to the root of your issue. Is there too much debris at the bottom of your tank? Is your filter old and no longer working as it should? Do you need to change an overused filter? Figure out the problem first. 

Once you have identified your tank’s issue, get to work on resolving the problem. Once you have either changed the filter, cleaned the bottom of the tank, and have replaced some of the water within the aquarium, give it 3-5 days to get back to normal.

If the problem persists after 10 days, go ahead and call your local aquarium experts and see if they have any further advice. It is likely that you will be able to get your tank back to normal, but patience is key.

How to Prevent a Bacterial Bloom

There are two things that can make or break your aquarium: the water quality and the amount of food you give your fish. 

Water does makeup over 93 percent of your tank, so it would make sense that its quality level is one of the most important focuses when it comes to keeping your tank free of bacterial blooms. Secondarily, excess food in a tank can really muck up your water and is a key player when it comes to feeding the fire of bacterial blooms.

Keep the Water Clean

When it comes to changing your water, it does not have to be such a daunting task. It is rare that you would ever change the entire tank’s water, so this is a task that is totally manageable. You want to change your water at least once a week. 

This does not mean emptying your tank, but taking out around 10-20 percent of the water and replacing it with a fresh batch. This makes changing water extra easy due to only a small replacement being made.

Also, make sure that you treat the water with water conditioners to remove any harmful chemicals or metals. Conditioners help to remove chemicals such as chlorine. Replacing just a small amount of water is enough to keep the good bacteria and manage the bad.

It is also extremely important that you pay attention to the functionality of your filter. You can have the best filter on the market, pay loads of money to get it, and pop it in your tank like the fish boss you are.

However, if you neglect to replace the filter media within it, you may as well have no filter at all. The filter media should be replaced on a monthly basis to aid in dissolving wastes from your tank’s. Without a properly functioning filter, you are asking for big problems. 

Do Not Overfeed Your Fish

With water cleanliness and upkeep being such a big aspect of preventing bacterial blooms, it is understandable that excess food present in the water would be something that only adds to a murky tank. 

So many times fish owners tend to overfeed their fish. By doing this, all the excess uneaten food either dissolves in the water or settles at the bottom. Once this happens, bacteria then have a food source and can start to grow at ghastly rates. 

Fish only need to be fed once a day, and some breeds even less than that. If you are feeding your fish at the right rate with little excess food given at the time of feeding but they are still not eating, look to changing the type of fish food. 

There are types of food like fish crisps that tend to dissolve at a slower rate and don’t immediately make a dash for the bottom of your tank. Sometimes fish can be picky, so work with your little guys to find what is right for them. 

If you find you have lots of excess debris at the bottom of your tank, don’t immediately run to dump the whole thing out and start from scratch. Simply work to get the bottom of your fish tank cleaned by clearing the rocks, cleaning them off, and adding them back to the tank.

Try to do this as gently as possible so you don’t agitate the water too much, but be mindful that this may cause your tank to become cloudy. However, it should dissipate within a few days.


In conclusion, bacterial bloom can be seen as “too much of a good thing” and should be treated as soon as possible. You can expect it to last between 2-4 days in new aquariums and 3-5 days in established aquariums. To prevent bacterial bloom, be sure to keep the water clean and avoid overfeeding your fish.



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