Fishbowl Adviser

Cloudy Fish Tank: Causes and How to Make Your Aquarium Clear

Having a cloudy fish tank happens often, but it also comes as a surprise for many aquarium owners and enthusiasts. But why does an aquarium get cloudy? Cloudy tank water is not just about having trouble with seeing your fish. There are many causes of cloudy aquarium water, and some of them can be harmful to your fish. So you need to make sure to find the cause of cloudy fish tank water and react accordingly.

Fish in cloudy water

Why Is My Fish Tank Cloudy?

So, why is my fish tank cloudy? There is no single answer or cause as to why you get a cloudy fish tank. It can be frustrating when the aquarium water gets cloudy and your fish disappear into its hazy fog, but it also indicates a problem you might not have noticed. And even though changing the water might seem like a solution, it can sometimes make things worse. Let’s take a look at some of the most common causes and their solutions.

Having White or Grayish Aquarium Water

If you’ve noticed your aquarium water looks like a glass of milk was poured into it, your fish tank might have some problems. Your aquarium water might still be transparent, but there is still a thick haze that makes the entire tank look fuzzy. Gray water might indicate a small problem with your gravel or something better like a bacterial bloom.

Gravel Residue

If the water gets cloudy right after (an hour or two) after you’ve filled the tank, the reason might be insufficiently washed gravel. While you set up your aquarium, it’s important to rinse all the substrate you plan on putting in your tank. If you’ve forgotten to do so, all you need to do is drain the fish tank water and rinse the gravel until the water you’re washing it with runs clear. That should resolve the problem.

You can first do just a 50% water change and remove some of the dust from the aquarium gravel. If that doesn’t work, you’ll have to change the aquarium water completely. You can also try adding a mechanical filter media that will trap the particles instead of you. Another great option is polishing pads that can be cut to fit most filters.

Dissolved Constituents

If the gravel is not the cause of your problem, another cause might be high levels of dissolved constituents in your newly filled tank. You will need to test the water for dissolved constituents like phosphates, silicates, or any heavy metals and check the water’s pH level as a part of your regular aquarium maintenance. If this is the cause of your problem, you can treat the water with conditioners or use reverse osmosis on the water. And make sure you regularly clean your fish tank.

Bacterial Blossom

If the cause of your cloudy water isn’t the substrate or dissolved constituents, then it might be a more serious problem with bacteria bloom. Bacterial blooms happen in cases where there is a population of bacteria that require organic compounds for food in the water. The cloudy water caused by bacteria bloom won’t happen immediately. It will appear days, weeks, or sometimes even months later. It takes several weeks or months to establish bacterial colonies in the water.

Unlike beneficial bacteria that you should have in your tank in order to get rid of ammonia, these bacteria are harmful to your fish. The heterotrophic bacteria you can see in the blooms can cause fish waste to rot and even produce ammonia. Heterotrophic bacteria can’t be seen with the naked eye, but there can be millions of them that can cloud the aquarium water.

How to fix a cloudy fish tank caused by bacterial bloom? All you have to do to fix this and prevent it from happening is with regular cleaning. You’ll need to keep the fish tank clean by doing partial water changes, removing any debris like uneaten food and decaying plants, and vacuuming the gravel regularly.

Cloudy Fish Tank

Getting Green Aquarium Water

Having green water is caused by algae growth. However, even though the cause may be a no-brainer, getting rid of it is not easy.

Light Exposure

One of the main causes of green water and algae problems is too much light. Exposing your tank to direct sunlight or leaving the room lights on for too long can cause algae growth. You’ll just need to reduce the amount of light your aquarium gets and move it somewhere out of direct sunlight.

Excess Nutrients

Having an increased amount of nutrients like nitrates and phosphates can also cause algae growth. Performing a water change can give you some immediate relief, but it won’t resolve the entire problem completely. You will need to deal with the nitrates and phosphates at their source to be completely free of them.

Phosphates can come from two sources:

  • A decaying matter like fish food
  • The water source

You’ll need to test the water you’re using for your tank and see if there are phosphates. If you notice a high level of phosphates, then the problem is with the water source and you’ll need to use a phosphate remover or reverse osmosis to treat the water. If the problem is decaying food, then all you need to do is cut back the feeding time to every second or third day.

Nitrates will naturally arise in the fish tank during time as a byproduct of fish wastes. The only way you can remove them is to perform regular water changes and make sure the filter is clean and adequate for the tank size.

Betta in cloudy water

How to Fix a Cloudy Fish Tank?

Nobody wants to have a cloudy fish tank – we all want to enjoy watching our beloved pets swimming. So how can you fix a cloudy fish tank? With proper aquarium maintenance and regular cleaning.

To prevent your fish tank from getting cloudy, you’ll need to do partial water changes, test the water, make sure you get water from a proper source, remove debris that appears in the tank, and vacuum the substrate.


  1. How to Fix Cloudy Aquarium Water: Causes & Remedies – Fish Subsidy


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