Why Is My Fish Tank Cloudy?

Do you look at other crystal-clear water aquariums, and wonder what you do wrong to make your fish tank cloudy?  Are you thinking of giving up fishkeeping because of your cloudy tank?

If yes, don’t.

Most fishkeepers go through the same problem and try cleaning the tank thinking that a dirty aquarium leads to a cloudy tank. However, they once again get upset when the water in a clean tank looks cloudy, even before adding fish.

There are a few reasons for a cloudy aquarium and some solutions.

All you have to do is read on. You will get your answer, solution, and learn a few things like how you can prevent a cloudy tank and what is a bacterial bloom!

Why is my fish tank cloudy?

The main causes of cloudy fish tanks are bacterial blooms, sand or substrate disturbance, fish breeding, coral breeding or snail breeding. Bad water quality can also be a contributing factor to a cloudy fish tank causing a bacterial bloom.

5 Reasons for cloudy fish tank water

There are various reasons for cloudy aquarium water.

1. Dissolved constituents

The most common reason is the presence of dissolved constituents like phosphates, silicates, and heavy metals in the water. You can check for its presence through a water test.

A high pH value proves its presence. However, it’s nothing to worry about.

You can resolve the problem either by treating the alkaline water with conditioners or start using RO water.

2. Bacterial bloom

A bacterial bloom is another reason for cloudy water in your aquarium. It appears a few days, weeks, or even months after setting up the aquarium. It usually happens when the new aquarium goes through the initial break-in nitrogen cycle.

It can also occur while reestablishing the tank after a large water change, medication cycle, or something similar which simply means even older more established aquariums can have bacterial blooms. However, this type of cloudiness usually clears up on its own.

Changing water won’t help much. It only makes the cycle last longer, and the bacteria take longer to grow to take care of their own.

There’s no need to panic about bacterial blooms.

It can be avoided by keeping the aquarium clean by removing debris like decaying plants and uneaten food, and by performing partial water changes.

Use flocculants to remove debris in the water, which you can’t remove via water change and vacuuming. Flocculants make the particles clump together to be easily removed by the filter.

Don’t forget to clean your filters too periodically!

3. Poorly rinsed gravel

Sometimes poorly rinsed gravel while cleaning the tank can cause cloudiness in a new aquarium. It’s because you end up releasing dirt and debris trapped in the gravel.

Resolve this by draining the tank and rinsing the gravel until you get clear water.

4. Restarted filters

The water can also get cloudy when you restart the filters after a shutdown. It’s because the resulting debris and tiny air bubbles create a white haze.

5. Certain supplements

Even supplements like bacteria, calcium, and ph adjusters can create a temporary milky white haze when added to water.

Why is my fish tank water green?

It’s easy.

Most of the time, green water indicates an algae bloom, which algae-eating fish don’t eat. The single-celled algae are suspended in water and are present because of high phosphate levels.

Now you may wonder where the phosphate comes from.

Well, it comes through the source of water. The chances are higher if you use well water because of phosphates in the fertilized soil leeches into the water. The water phosphate level won’t affect your health. However, it can accumulate in the aquarium to fertilize algae blooms, and lead to other problems.

The best thing preventive measure is shifting to another water source like RO (reverse osmosis) filtered water.

Even decaying matter like fish food makes a rich source of phosphate, in the green water. Reducing the amount of food you feed your fish or using a brand with less phosphate resolves the problem.

Lighting can also make water green because it affects surface water and algae. Lights kept continuously on for 8-10 hours naturally overfeeds the algae. Even 6-8 months old bulbs produce a degraded and more yellowish light that isn’t useful for plants but feed algae.

So reducing the light duration and buying new bulbs can prevent green water.

Why is my aquarium water yellow?

It’s because your fish tank is dirty with overcrowding, overfeeding, and high ammonia or nitrite levels. The best solution is getting a larger tank, reducing the number of fish in the tank, or getting a larger and more powerful filter.

A good filter with carbon or some other chemical neutralizer filters the water well and removes organic pollutants to prevents water pollution.

Why is my aquarium water brown?

It depends on the fish in the aquarium. Some fish are used to living in environments, usually forested areas without much water flow. The water is naturally brown because of the leaves, wood, and organic matter in the water release tannic acid that dyes the water brown.

These fish need the same water chemistry, which is created in the water tank by some additive materials.

However, brown water is ugly if you don’t have this type of fish in it. The water turns brown if driftwood in the aquarium is too soft or isn’t adequately pressure-treated.

Replacing the wood helps, and having a filter with carbon helps remove the watercolor and granules.

Is cloudy water bad for fish?

No, cloudy water isn’t harmful to tank inhabitants. It can clear on its own.

How Long Does It Take for Cloudy Aquarium Water to Clear

Cloudy water clears in a few days. However, do consult your aquarium fish specialist if it doesn’t clear within ten days.

Why do bacterial blooms occur?

Overfeeding, dead fish and plant matter are the main reasons that trigger a bacterial bloom. They increase the reproduction of heterotrophs, which naturally decompose organic waste. The quick reproduction leads to the increased heterotrophs attaching to the surface to cause a bacterial bloom.

How do I get rid of bacterial bloom in the aquarium?

Bacterial blooms usually disappear in a few days, but you may, at times, have to intervene. The quickest option is to introduce an enzyme or beneficial bacteria to the water to find the bacterial bloom quickly disappearing. Just make sure you follow its instructions.

There are some other options you can also try out:

Check and see if your aquarium filter is broken, blocked, dirty, or malfunctioning. If yes, fixing it removes the bacterial bloom overnight.

1. Change the water

If it’s been some time since you have changed the tank water, changing it helps. It eliminates excess nutrients in the water. However, do make sure you vacuum the substrate to remove organic material.

2. Reduce fish feed

Too much food in the water helps bacteria to flourish.

Fish usually eats their food in about 2 minutes. So if you find food hanging around after 5 minutes, it’s a sign that you are overfeeding. Reducing the feed and clearing out the excess food helps.

Why is my fish tank cloudy after cleaning?

Well, it’s surprising to learn that there are so many reasons for a clean fish tank to get cloudy water!

Water changes

Yes, water changing does make the water cloudy. It’s because the water you siphon out loosens the gravel and releases any trapped dirt. The gravel is further disturbed and loosens more debris when you pour fresh water into the tank.

The best way to reduce the amount of debris agitation is by placing a shallow bowl at the bottom of the tank. Then pour water into it instead of pouring water directly on the fish tank bottom.

Trapped sediment

Even the cleanest fish tank has some trapped sediment, dirt, and debris. Disturbing the gravel leads to the waste entering the water and creating a cloudy appearance.

It’s avoided by minimizing gravel movement, while regular filtration takes care of the cloudiness in a day or two.

Why is my fish tank cloudy with no fish?

This is another common question people ask, and the culprit is none other than a bacterial bloom.

As mentioned earlier, it’s a cluster of heterotrophic bacteria that create a slimy biofilm on the water surface. And it’s common even in tanks without fish.

Other causes

Moving or shaking the tank may disrupt the bacterial colonies in it, leading to bacterial loss. The tank goes cloudy while the heterotrophs re-establish the bacterial colonies.

Even adding antibacterial medications can lead to bacterial colonies.

Excessive tank cleaning

Even over cleaning of the tank eradicates many bacterial colonies. It, in turn, makes the heterotrophs work at reproducing enough bacteria to sustain the bank’s nitrogen cycle. 

Added livestock

Adding large amounts of livestock makes your tank’s bacterial colonies try and reproduce every 20 minutes to convert the additional produced waste.          

Adding a dirty substrate

Adding a poorly cleaned new substrate can make the water tank go cloudy.

How to get crystal clear aquarium water

Every aquarium owner wishes to have crystal clear fish tank water, and there are various ways to get it. here is a brief description of the different available options.  


Filtration helps move and clean the tank water and make it safe for fishes. There are three main options available, with their individual features and benefits. Here’s a brief overview of each type:

1. Mechanical filtration

It involves the physical trapping of dirt and debris in the filter’s sponge, filter wool, or both. Finer sponges trap smaller particles while filter wool or floss traps fine particles to polish the water.

Just make sure you have a suitably sized filter for the fish tank’s size.

Using either two filters with polishing pads or a more prominent model gives cleaner water. Don’t forget to regularly throw and replace the old and clogged filter wool and polishing pads with new ones for better filter performance.

2. Chemical filtration

Activated carbon is the best chemical filter that sucks up dyes, medications, odors and other impurities to give crystal clear water. It’s available as loose granules, in net bags, or impregnated filter sponges designed to fit specific filter makes and models.

Carbon should be changed once a month to prevent it from getting saturated and lose its effectiveness.

3. Biological filtration

Certain bacterial strains or aquarium plants are used here to consume toxic ammonia and nitrogen compounds from the water. The beneficial bacteria grow on any surface, including the aquarium walls and gravel. Many filters exist as high surface area biomedia or bio-rings providing more space for bacteria to thrive.


Some fish like goldfish and cichlids are messy feeders that eat lots of food and produce lots of physical waste. They also dislodge and eat fish poo and uneaten food from the substrate. They give the best results if accompanied by suitably sized filter units.

Food type

The type of food you feed your fish also affects the water clarity.

Large, protein-rich foods like catfish tablets and mussels can cause suspended particles that degrade water quality. It’s better to use a good flake food.

Just be careful and make sure you don’t overfeed your fishes and use a net to remove uneaten food.

Proper maintenance

Proper maintenance goes a long way at ensuring crystal clear water!

It involves regularly cleaning filters, vacuuming the substrate, and removing any bodily waste in the system. Changing the water once a week also helps minimize nitrates, stabilizes pH levels, and promotes fish growth.


As mentioned earlier, flocculants clear water by clumping tiny particles together into bigger particles that are easily filtered and removed.

Tips for preventing bacterial bloom

Prevention is always better than cure, even in the case of bacterial blooms. The preventive tips are similar to the treatments and generally involve:

  • Ensuring the aquarium filter is working properly
  • Removing dead plants, fish and uneaten food
  • Adding enzymes and beneficial bacteria if necessary
  • Regularly changing water and cleaning the substrate
  • Conducting water tests to monitor the water’s nitrate and phosphate levels

How to prevent cloudy fish tank water

Here is some preventive measure that helps prevent fish tank water from getting cloudy:

No overfeeding

You may be eager to feed your fish, to ensure they don’t go hungry. However, did you know that fish don’t naturally eat every day? And that some predatory fish eat only once or twice a week?

So don’t worry! Fish won’t starve in just three days!

Excess food only ends up making the water cloudy.

No overcrowding

Too many fish in the fish tank lead to more waste and food for microbes to lead to cloudy water. It also increases the water’s ammonia and nitrite levels.

Add activated carbon to the filter.

Adding activated carbon media or carbon pads to the filter clears the water and absorbs nutrients that feed bacterial bloom.

Seed the aquarium

If there’s a healthy and well-established fish tank you can access, add a few handfuls of its gravel to yours. The procedure is called seeding, where it seeds beneficial bacteria to speed up the clearing process.

Test the aquarium water

Test the water for ammonia, nitrite, and phosphate levels once you notice it is cloudy. Don’t worry. In most cases, the levels will be zero.

Water clarification

Liquid and tablet water clarification products help clear the water. All it takes are adding a few drops or a tablet to the water, and it clears up. They attract the dust and dirt in the tank to form larger clumps that get carried away into the filter. It works even better with an additional filter.

Now, do you still feel like giving up on fishkeeping?! You have the solution, and preventive tips, to ensure your fish tank water doesn’t get cloudy anymore! Adopting them will ensure you end up with a crystal clear aquarium you will be proud of!

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