You look in your tank and go:

“What’s going on with my water? It’s cloudy!”


For most people, cloudy water is NOT what you want in your beautiful aquarium.

Besides hiding the fish, it can restrict plant growth and generally make your tank less enjoyable.

So, how do we beat this problem?

Understanding the causes is the first step to finding the solution.

Let’s get into it!

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Causes & Solutions for Cloudy Water

There are three main types of cloudy water.

Cloudy water can be foggy white, green or more of a murky brown.

1. Bacteria bloom

This makes the tank look like someone poured milk in your aquarium.

Sometimes an entire gallon of it.

This type of cloudy water makes the tank look hazy white.

If it is just beginning, there might only be a slight “mist.”

Bacteria blooms generally occur when the tank is still cycling.

Left alone, they should go away in a week or so.


As much as you might want to, it is usually advisable NOT to change the water in this timeframe as it prolongs the outbreak.

(It has to run its course.)

But what if your tank isn’t new?

There may be another cause.

Overfeeding can cause bacterial blooms, as can dirty gravel.

(Testing the ammonia is a good idea.)

Some people also notice their water will go cloudy if they leave too many rotten veggies in the tank.

Cleaning the aquarium by performing a gravel vacuum and doing 30% water changes 3x per week is a good idea, as well as removing dead or decaying matter such as rotten plants and uneaten food.

If the tank has fully cycled and its been more than a few weeks struggling with this issue – despite trying the above remedies – you may wish to try another approach.

A quick fix is a UV sterilizer.

The UV sterilizer eliminates the bacteria in the water that cause the bloom, rapidly making the water clear again in a matter of days.


The best part?

It will also help if you have the following problem, the second cause of murky water in your goldfish tank…

2. Suspended algae bloom

A suspended algae bloom (also known as green water) will cause the water in the tank to turn a frightening shade of bright green.

Cloudy water that is slightly green or mostly white can be a precursor to green water, when the entire tank turns into split pea soup.

The green you see is actually made up of millions of single-cell phytoplankton algae particles.

Some people actually like green algae as it is nutritious for the fish and helps to purify the water.

But for the average hobbyist?

They want to actually be able to SEE their goldfish swimming around in their aquarium – not just stare into a swamp!


What causes this kind of cloudiness?

Too much light can cause green algae blooms.

Reducing the light to around 6 hours a day may prove useful…

… As well as shielding the tank from direct sunlight.

Too many phosphates in the water can also be a problem.

If that is the case, phosphate removers such as SeaChem PhosGuard can remove the food source of the algae.

But the issue is when you have to do a water change, the new water will introduce more phosphates. 🙁

So you’re continually having to treat the water and replenish the PhosGuard.

Don’t want to do that?

You could change your water source by implementing RODI water filtration.

Not only is that pricy, but you will have to replenish all the minerals the process removes.


As mentioned in the above section, a UV sterilizer will quickly knock out the problem no matter the cause and save you of having to go down the rabbit hole of shotgun solutions.

3. Suspended Particulates

Goldfish eating food

Food (especially when overfed) can cause little particles of the food flying all over the place to make the water murky.

This can be the case when the fish are being fed large amounts of messy food they aren’t able to eat before it gets trapped in the substrate, filter or water column as tiny particles.

Another possibility?

Substrate like sand or gravel that has not been properly washed can release the fine dust into the water column.

For suspended particulates causing hazy water, a sponge filter is an excellent remedy.

Squeezing it out every 12 hours is also a good idea until the cloudiness subsides.

Within about 3 days it should be mostly if not totally vanquished.

The fine pores in the sponge filter trap the tiny particles that make it difficult to see through the water as it draws water through its surface.

And sponge filters are great for goldfish tanks anyways

4. Tannins

Does your fish tank have a darkish brown tint to it, like someone poured black tea in your aquarium?

If that’s the case, chances are your aquarium looks cloudy brown because of something called tannins.

In the fish tank, this usually comes from two things:

  1. Driftwood or other submerged wood that has not been properly cured first
  2. Soil that has been added (used commonly in planted tanks)

To fix the problem you will have to either go the short or the long route.

The short route is to remove the stuff from the tank that is leaching into the water and perform a huge water change.

Short for the tank that is.

Because if you want to put the driftwood back in, you will probably have to soak it in another container until it finishes releasing the tannins. Boiling is said to help speed this process up.

For soil, chances are if you put it in the tank you want it there – you just don’t want the tannins 🙂

Aside from performing water changes until it settles down (yeah, that’s the best way to remove those tannins when your water looks yellowish)…

… One useful tip is to include some activated carbon in your filter.

The charcoal should be replaced regularly as it becomes exhausted.

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Cloudy water can be a pain to deal with, but the good news is it is entirely treatable, and with the right approach can be cleared up in a relatively short amount of time.

Getting rid of it is totally possible – and will definitely give you a feeling of triumph 🙂