Cloudy water is normal in a new fish tank that has just been cycled. It is also normal for the water to become cloudy after the addition of a new plant. However, you might be alarmed to find your fish tank water suddenly became cloudy overnight. There are a couple reasons why your fish tank water suddenly became cloudy, and in today’s article we will explain those reasons and ways to prevent them from happening in the future. 

Fish tank water got cloudy overnight

The main reasons fish tank water gets cloudy overnight is overfeeding, decaying plants, algae growth, bacterial bloom, and dusty substrate.

Overfeeding

The most likely reason your fish tank water suddenly got cloudy overnight is because you are overfeeding your fish. When you overfeed your fish, two things can happen. The first is that your fish consume all the food, which in turn causes them to poop a lot more than usual. Your fish tank is not prepared to handle all of this waste, and as a result it can add ammonia to the water and make it cloudy. Secondly, your fish might not eat the excess food, and it will float to the bottom. The excess food will attract bacteria to from around it, which in turn can make your fish tank water cloudy. 

Decaying plants

Decaying plants is another cause of cloudy fish water. Once plants die and start to decompose, organisms consume the nutrients. These organisms can produce a wide range of bacteria that can make your fish tank water cloudy. Adding plants to your fish tank can also switch up the water chemistry, and cause more nitrogen to be released into the water, making the water cloudy as well. 

Algae Growth

Algae is another common reason fish tank water will get cloudy overnight. When algae starts to grow in your fish tank, it can start to hog all of the light that comes into the tank. This in turn causes the algae to grow at an alarming rate, and release nitrogen in the process. An overconcentration of nitrogen in your fish tank can turn the water cloudy. 

Bacterial bloom

If you have a new fish tank, the cloudy water is most likely a result of bacterial bloom. This is very common in new fish tanks, and it is caused by the rapid increase in bacterial colonies inside the fish tank. There is no reason to stress about bacterial bloom because the cloudiness usually goes away after a couple days. 

Gravel/Substrate

If you don’t properly clean your substrate, it can cause your water to get cloudy. While the cloudiness usually appears immediately, it can cause the water to turn cloudy overnight. If you suspect this is the issue, you should check out my article on what to do if you forgot to rinse gravel for your fish tank.

What to do if your fish tank becomes cloudy overnight

There is no need to panic if your fish tank becomes cloudy overnight. The first thing you should do is wait a couple hours to see if it clears up. If it stays cloudy, then we recommend doing a water change. If that still doesn’t clear up the water, you should extensively clean the gravel in the tank if you have any. Remember to always thoroughly wash any item before you place it inside your fish tank.