Dealing with Cloudy Water in the Fish Tank – Restoring to its clean & clear state

The main point of keeping goldfish for display is to be able to see them clearly through the fish tank, so that we can admire their beauty and grace. Imagine just as we are getting used to enjoying that, then one morning we woke up and something changed… Cloudy water in the fish tank!! What happened? Why???

Imagine that although the goldfish are still visible, it seemed as if the cloudy water in the fish tank is the only thing we could see. Oh No! It has taken away the enjoyment of watching our goldfish! What can we do? Can we ever restore it to its clean and clear state?

Clean & Clear Fish Tank
Clean & Clear State of the Fish Tank

Well really, you do not have to imagine this scenario. It is very common in the fish keeping hobby. Understanding the types of cloudy water and their potential causes will help us to deal with them.

What is cloudy water?

This is basically the state of the water where it is not clear. Cloudy water in the fish tank can appear milky or/and with coloration. Whichever it is, it obstructs your view to what is in your tank, such as your beautiful goldfish. Depending on what is the cause, some cloudy water is detrimental to your goldfish.

Cloudy Water In The Fish Tank
Cloudy Water In The Fish Tank

Types of cloudy water

There are many types of cloudy water. Oh yeah… there are the white or grayish ones, the brown or tea-like ones and the green one. Let us take a look at what causes them.

1. White/Grayish Cloudy Water

When you encounter a milky white or grayish cloudy water in the fish tank, the possible causes are bacterial bloom and suspended particles.

Bacterial Bloom

The bacteria here refer to the beneficial nitrifying bacteria that are involved in the Nitrogen Cycle. In situations where these beneficial bacteria are building or re-establishing their colonies so that they can handle the amount of wastes in the tank, bacterial bloom happens and causes the water to be cloudy.

A few typical situations that affect the bacteria colonies and causes bacterial bloom are:

a) You have just set up your fish tank and it is cycling.
b) You have just done a big water change and filter maintenance.
c) You have not turned on your filter for a while, and the bacteria colonies have depleted due to lack of oxygen.
d) You have just added a few fish into the tank.

The cloudy water caused by bacterial bloom is not detrimental to your goldfish. However, if there are Ammonia and Nitrite in the water, these will be bad for them. So please do a water test to check. If Ammonia and Nitrite exist in your tank, you will need to do a partial water change.

The cloudiness will go away by itself with time when the bacteria colonies are established. You will just need to bear with it for a while.

Suspended Particles

White or grayish cloudy water can also appear when suspended particles or debris from substrate, rocks or decorations are introduced into the tank. This happens when we did not rinse and clean these items properly before putting them in.

Besides that, these particles and debris can be stirred up accidentally during our fish tank maintenance as well.

This type of cloudy water will not affect your fish, and will slowly clear itself when the suspended particles and debris are sucked into the filter or when they settle to the bottom of the fish tank.

2. Brown/Yellow Cloudy Water

Brown or yellow cloudy water which looks milky are usually caused by dissolved organic matter. If it looks more tea-like, then the likely cause is tannins.

Dissolved Organic Matter

Milky brown cloudy water in the fish tank is usually due to dissolved organic matter such as fish waste, excess food, decaying plants and dead inhabitants. This happens with over-feeding, not doing enough fish tank maintenance and dirty filters. If this is not dealt with, it will cause a spike in toxic Ammonia and Nitrite.

You can clear this off by removing any excess food, decaying plants, and dead inhabitants; and do a big water change (25-50%). Activated carbon or Purigen can also help to speed up the process.


If the cloudy water is more tea-like with yellow coloration instead, the cause is most probably from tannin which is an organic substance from driftwoods or dried leaves. Although it is not dangerous, it will lower the pH of the water.

You can use filter media such as activated carbon or Purigen in your filter to clear up the water.

3. Green Cloudy Water

The green in green cloudy water are algae.

The reason why there are so much algae in the tank is because of high concentration of nitrate and phosphate in the water, and too much of light. High nitrate usually indicates too much of feeding and not enough of water change.

Some goldfish breeders keep their goldfish in green cloudy water as they contain a lot of nutrients. So it is not dangerous for them, but it certainly looks terrible if you are keeping a display tank.

So to deal with green cloudy water in the fish tank, limit the amount of light that the tank gets or block it out completely, do a major water change of 25-50%, and stop pampering your goldfish with too much food!


Cloudy water in the fish tank can occur anytime when the conditions are right. Some of them are not so much of a worry as they are not dangerous to our goldfish but are more of an eye-sore. However there are also those that serve as indications that the water quality is becoming toxic, so you better get your a** off that couch and do something about it!

With an understanding of why cloudy water happens, we can deal with them accordingly… and that is important in order to restore our fish tank to its clean and clear state. How else can we enjoy our goldfish, right?

Share this:

6 Replies to “Dealing with Cloudy Water in the Fish Tank – Restoring to its clean & clear state

  1. Hello Alex,
    Thank you for this very informative article.
    I don’t have a fish tank but I know someone who has a huge one. I know it is a lot of work to maintain healthy fishes in a healthy environment.
    Anyway, i now understand better on what is going on in the fish tank. I believe if i have a fish tank, I would be working hard to keep it clean. It is so peaceful to look at the fishes in this environment.

    In your article you talked about ammonia and nitrite, do you have a special tool to measure their rates in the fish tank? or do you just know by experience and would change 50%-60% of your water if you suspect there’s any Ammonia and Nitrite? Thank you and good luck.


    1. Hi there,
      Thanks for the visit. It is indeed hard work to keep a clean, clear and healthy fish tank.

      On Ammonia, Nitrite and Nitrate, it is best to use a water test kit to know the condition of your tank water. The one that I am using is the API Freshwater Master Test Kit and I think it’s great.

  2. It is so good to come across this site and post as my dad loves his fish and his massive fish tank but might not know how to combat that murky water when it creeps up. I love how you outline what causes it and ways to stop it in its tracks. Thank you loads for this!

  3. Wow, there is a lot to consider having a goldfish tank. I think it is a good article because I have seen some tanks where the water was crystal clear and it looks marvelous. All this time I thought the pumps and filters would not allow any cloudiness to happen. Thanks.

    1. Hi Ronnie,
      Thanks for the comment. I guess that’s the point of keeping fish for display, ie having a clean and clear tank. 🙂
      Having a good pump or filter do help, but it still require regular maintenance.

Leave a Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.