Why is There a White Cloud in Fish Tank?

The serenity of a freshwater aquarium is amazing. The beautiful clear water, the twinkle of the gravel, and the bright colors of your fish are awesome. But what happens when you wake up, go to your aquarium and instead of crystal clear aquarium tank water you see a white cloud. What happened? The water was crystal clear last night.

Gold and white goldfish in a fish tank
Is a white cloud in the fish tank water cause for concern?

Does your aquarium have a white cloud in it? Are you wondering if the cloudy water is something that you should worry about? Most people without experience would probably freak out if they started a new tank, added a few new fish, and bang, one morning they wake up and their finned friends were swimming in a white cloud.

Thankfully there really is no reason to worry when you find a white cloud in your aquarium. That’s because this isn’t a big problem and can be solved easily. Actually, in many cases it might even go away on its own. In this article you’ll learn the 2 primary causes of cloudy aquarium water, the implications of it, and what to do about it.

Table of Contents

What causes cloudy water in a fish tank?

There are two common reasons for this condition in a freshwater aquarium. The good news is that neither of these reasons are dangerous to your fish.

White foggy aquarium water tuned into clear water
A white cloud in your aquarium can be quite concerning.

1. Bacterial Bloom

The most common reason for white cloudy aquarium water is a bacterial bloom or a rapid growth of bacteria. This is more common in an established tank verses a new aquarium. Bacteria does not necessarily mean anything bad is happening. As you are well aware, bacteria is everywhere. A fish tank actually relies on the presence of bacteria to run properly. This is because they help to break down waste products created by your fish and plants. These little guys are called beneficial bacteria. They grow in the aquarium filter media, in gravel, on decorations, and other surfaces. The waste products created by your freshwater fish are nutrients for beneficial bacteria. Yes, fish waste is important to the ecosystem that forms in your aquarium. The waste products of bacteria are in turn seen as nutrients for the plants in the aquarium. Sometimes as new fish are added to a tank, which brings new nutrients for bacteria, the existing bacteria can start to grow at extreme speeds and therefore make the water in your aquarium look like a white cloud.

2. Dusty Gravel

The second most popular reason for the white cloud in your aquarium water is insufficient cleaning of new gravel. We’ve had many patients mention this and it’s not surprising to have this happen to newer aquarium owners. New gravel is covered with dust from when it is made and transported to your local pet store. A big “must do” is that you must rinse it before putting inside your fish tank (more on this here in our How to setup an aquarium guide). If you don’t rinse the gravel completely of the dust it came with, all those dusty particles will float up as you fill the tank and voila, you have cloudy aquarium water.

How can you tell what is making your tank water cloudy? If you recently added gravel, it could be either of those reasons. This is because new gravel is also a perfect place for bacteria to grow. Normally if the water is cloudy because of dust from the gravel, it will settle in less than a day. If it stays cloudy for more than a day, it is most likely a bacterial bloom.

How to clear cloudy aquarium water for good?

If you have come to the conclusion that your water is foggy because of a bacterial bloom (which is the most common cause of cloudy water), then there is nothing much to do. The water in your fish tank will become clear within two to three days. You can however, check the oxygen level in your fish tank. There’s no special test needed to check. Just check whether the fish are gulping for air, moving their gills rapidly, or are becoming inactive. If your aquarium fish show any of those signs, you can turn the air pump on for a prolonged amount of time or replace part of the tank water by using a bucket to remove a portion and then dumping in some clean water.

If however, you suspect that the root of the problem is insufficient cleaning of the new gravel you just put in, you can try to remove it for cleaning. This is a very common problem in a new aquarium. Rinse it thoroughly and put it back. It’s a lot of work for sure. But it will make the aquarium environment much friendlier for your fish. It’s fine to leave it in and wait until white cloud of dust particles settle down and the water becomes clear.

Please keep in mind that the cloudy tank water will become foggy each time you do a partial or full water change. When you replace water or rearrange the gravel, the dust that had setted to the bottom will be disturbed and you’ll have a cloudy fish tank again though the effect will fade over time. That’s because the dusty particles are still in your fish tank, they just settled to the bottom. Yes, some of it will get trapped in your filter, but since most of it settled to the bottom of the fish tank everytime you disturb it, the cloudiness will return.

So, while it may look concerning, we cannot stress enough that in most cases, cloudy water is not a problem for aquarium fish and the other inhabitants in your fish tank. As long as the fish have enough oxygen, your tank mates will be fine and the aquarium water will soon become clear with no damage done.

Now that you know what causes a white cloud in fish tank, you can take the appropriate steps. Thus you will be happy and your pet fish will be happy. And keeping your Pet happy is what we all want.

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