Cloudy Goldfish Tank (Causes, Prevention, Treatment & More)

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Last Updated on 2023-05-24

If you’ve looked into your goldfish tank and noticed that it’s become cloudy, don’t panic! In most cases, it’s going to be more annoying for you than it is for your fish. Fortunately, if you do have a cloudy goldfish tank, there are a few things you can do.

Keep reading this article to find out what causes a cloudy tank, how to treat it, and even more importantly, how to prevent it!

What Causes A Goldfish Tank To Become Cloudy?

There are a few different things that can cause your goldfish tank to become cloudy. And based on the color and timing of when it happens, you can often figure out what’s causing it. If your fish tank is cloudy, then it’ll either be grey/white or green. Let’s take a look at what can cause grey/white cloudy water.

What Causes Tank Water To Become Cloudy Grey/White

There are a few different causes behind this, and some of them are a lot more simple to figure out than others.

You May Have Disturbed The Gravel Too Much

Did you notice that the water became cloudy after you cleaned your tank or changed the water? If this is the case, then the chances are it’s caused all the muck, bacteria, silt, and debris in the gravel to be kicked up into the water of the tank.

Fortunately, you won’t need to do anything if this is the case. Simply leave the tank, and it will all settle back into the gravel. In fact, it’s often a good idea to disturb the gravel on purpose before changing the water so you can siphon out as much muck as possible.

A Bacterial Bloom

Another common cause of cloudy water is bacterial bloom. While it’s most likely to happen in the first few days, bacterial blooms can happen weeks or months after you’ve set your aquarium up for the first time.

Chemicals And Heavy Metals

Lastly, chemicals and heavy metals can also cause the water in your tank to become cloudy. This is most often the case if you haven’t used a water conditioner before adding new water to the tank. Remember, adding a water conditioner is extremely important. When you don’t add water conditioner, the heavy metals and chemicals can quickly become fatal to your goldfish.

What Causes Green Cloudy Water?

If water is green and cloudy, then it’s obviously one thing—an algal bloom. However, while you know what it is, there are a number of different things that can cause it. Here are some of the reasons an algal bloom can occur in your goldfish tank.

Too Much Light

If there are algae in your tank, then one thing is certain. You’re letting too much light into your tank. This is most common in tanks that are in front of a window or where sunlight is constantly getting to them. However, it can also occur when you’re leaving the tank light on.#

There’s Too Much Waste In The Tank

Waste to your fish is nutrients to algae. If you’re not changing the water in the tank often enough, or you don’t have enough live plants, then algae can begin to bloom. It’s normally nitrates that are produced from decaying waste that cause this to happen.


Lastly, as well as too much waste, phosphates can also cause algae bloom in your tank. Phosphates normally enter your tank through your tap water, and if you notice algal blooms, you should test your tap water to see how many phosphates are in it.

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How To Fix A Cloudy Goldfish Tank

Here’s the good news! There are plenty of ways you can fix cloudiness in your goldfish tank! However, the way you treat a cloudy goldfish tank really depends on what’s causing it! Here are all the ways you can turn your tank’s water crystal clear again!

How To Fix Cloudy Water That Is Grey Or White

Here are all the different ways you should treat water that is cloudy grey or white.

Leave It Alone

If it’s being caused by a bacterial bloom, one of the best things you can do is simply leave it alone. Grey cloudy water, as caused by bacteria, is actually the tank stabilizing itself. You need bacterial colonies in your tank to remove all the ammonia, nitrates, and nitrites in the tank!

When you leave the water alone, it will oftentimes clear up quicker than if you keep trying to change the water, clean the filter, etc.

Wash Gravel Thoroughly

If you’re just starting your tank out, then you may want to consider emptying it and then washing the gravel thoroughly. Doing this will remove as much of the silt as you can from it, so next time you add water, it won’t stir the tank up so much.

Just be warned, you shouldn’t do this if your goldfish is already in the tank. Instead, do this only if the tank hasn’t been cycled yet.

Change The Water

If you know that the cloudy water is being caused by dirt or silt, not bacteria, then you’ll want to change the water. It’s best to remove around 15-30% of the water, depending on the severity, but never more. Removing more can shock your fish as it’s likely to change the water parameters.

As well as changing the water, you should also remove any rotten food and vacuum the gravel as well.

Clean The Tanks Filter

If the filter hasn’t been cleaned in a while, now is a good chance to give it a good wash. When you’re changing the water, siphon it into a bucket. Once it’s been siphoned into the bucket, remove the mechanical filter (the spongey part) and squeeze it out. You should keep squeezing it out and shaking it around the water until it looks clean.

As well as this, you should also take the opportunity to change the chemical filter if it needs it. (It should be changed at least once a month.)

Add Water Clarifier Or A Water Polisher

Lastly, you can also add a water clarifier or use a water polisher if you think that the cloudiness is being caused by debris.

If you’re not sure what those two are, a water clarifier is a solution you add to the tank. It clings to debris and material, making it much easier for them to be filtered.

A water polisher, on the other hand, is placed inside the filter. It’s similar to a mechanical filter; however, the holes are a lot finer. These fine holes trap more debris, giving your tank crystal clear water!

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How To Deal With Green Cloudy Water

If your water is cloudy and green, then you’ll need to focus on removing all the algae that’s floating about. Fortunately, there are plenty of solutions and ways to deal with cloudy green water!

Add More Live Plants

One of the simplest ways to reduce cloudy green water in your goldfish’s tank is to add more live plants. One of the reasons algae often blooms in tanks is because there are lots of nutrients in the water and no competition.

By adding live plants into the tank, you’re going to be adding more competition! Your goldfish are going to love it, too, as it will keep them entertained and make the tank feel more natural!

If you’re not sure what plants to go with, anubias, java fern, and Cabomba are a few great choices.

Add A Few Algae Eaters

As well as adding plants you can also eat algae eaters into your tank as well! Snails are the most natural choice as they feed primarily off algae; however, you can also add certain species of pleco too.

Luckily, goldfish are also algae eaters, and they’ll help remove some of the algal bloom too!

Reduce The Amount Of Light Entering The Tank

You should also reduce the amount of light entering the tank. Especially sunlight. If your tank is near direct sunlight, you should move it somewhere it’s more out of the way. If you can’t do this, try placing a towel over it during the day to reduce any sunlight getting in.

You should also make sure you’re not leaving the lights inside the tank on all the time as well. And if possible, reducing the time you leave them on for. 4 hours a day for a few days will be fine for your goldfish.

Remove Any Waste

Algae receive nutrients from food, fish waste, and anything else rotting in the tank. This is because rotting organic matter releases nitrites and nitrates, which algae feed off. If you’re suffering from an algal bloom, you need to be on top of this and make sure you’re removing as much waste as possible.

Once you’re done feeding your goldfish, check the tank. Whatever they haven’t eaten, scoop out with a net and throw away. Aside from this, use your gravel vacuum to disturb the gravel and kick up waste before performing a water change to suck as much up as possible.

Try A UV Steriliser

While you may think UV light is going to increase the amount of algae particles in the tank, it’s going to do the opposite. Adding a UV sterilizer to your tank is going to help remove a lot of the algae causing cloudy green water.

However, on its own, it won’t be completely effective, and you’ll still need to combine it with other methods as well!

Algaecidal Chemicals

If you don’t have patience, you can try using certain algaecidal chemicals. The only one I’d recommend, though, is API Aquarium Algae Remover. It’s been designed specifically with aquarium algal blooms and green cloudy water in mind, and it’s completely harmless to fish.

However, before using it, make sure you read the instructions to make sure you don’t overdose the tank.

Phosphate And Nitrate Filter Media

Phosphate filter media and nitrate filter media are other great options. If your filter has enough space for them, they can be a brilliant way to stop green cloudy water in your goldfish tank. However, you do need to be careful.

You don’t want to remove too much nitrate as it could end up affecting the natural bacteria colonies in your tank.

How Can You Prevent Cloudy Water In Your Goldfish Tank?

If you’ve sorted out the cloudy water in your tank, you definitely don’t want it to happen again. So here are a few ways you can prevent it!

Don’t Overstock The Tank

First of all, you definitely don’t want to overstock your fish tank. Remember, goldfish need 30 gallons for one and then 10 gallons for each additional goldfish. If you plan on adding other fish to the tank, make sure you know how much space they need.

If you overstock your tank, then you’re going to increase the amount of waste being produced, and if your filter isn’t powerful enough, it won’t be able to remove it all. And on top of this, it will just make your goldfish unhappy.

Change The Water Frequently

Making sure you’re changing the water is also going to reduce the chance of a cloudy tank. Especially if an algal bloom is the problem. When you change the water, you’re going to be removing a lot of the nutrients that feed algae. Without these nutrients, it’s not going to be able to grow nearly as fast.

Don’t Overfeed Your Goldfish

If you’re overfeeding your goldfish, then there’s going to be more waste in the tank than there should be. This could be because the food you’re putting in goes uneaten or because your goldfish starts producing a lot more waste.

When you’re feeding your goldfish, don’t feed them all at once either. Instead, give them 2-3 meals a day. When you give them this many meals, you’ll be able to see better how much food they’re eating and how much is being wasted.

And if you feel bad, remember, fish don’t eat every day in nature, and your goldfish can even cope going a couple of days without food!

Make Sure You’re Changing The Filter And Cleaning It

The filter in your tank is essentially what keeps it clean in between water changes. Because of this, you want to make sure you’re keeping it clean and changing the media whenever necessary. The chemical filter should be changed every couple of weeks, and the mechanical filter should be washed every time you change the water.

Use A Seed Filter (Where Possible)

If you already have an established aquarium, or you know someone who does, using a seed filter is a great way to reduce the chance of cloudy water. To do this, simply take some of the biological filters from the established tank and place them into the new tank.

When you do this, you’re transferring the good bacteria from the old tank into the new tank, which is going to reduce the chance of cloudy water occurring dramatically! If you can’t add a new filter, you can also try adding gravel which also houses bacteria.


Here are some more commonly asked questions!

Why Is Goldfish Tank Cloudy After Water Change?

If your goldfish tank is cloudy after a water change, it’s most likely due to the fact adding water has kicked up all the silt and muck from the gravel. If this is the case, it should settle down after a few hours.

If it’s more than a couple of days, then it’s probably a bacterial bloom. Just remember, bacterial blooms can happen months after a tank has been set up, so don’t worry too much.

Why Is Goldfish Water Cloudy After One Day?

Although it’s unlikely, the goldfish water could be cloudy after one day because of a bacterial bloom. More likely, though, it could be something to do with the water you’re using. Remember, when you’re adding water to the tank, you need to make sure that you’re using a water conditioner as well!


Now you know why your goldfish has a cloudy tank! And fortunately, as you can see, in most cases, it’s nothing to worry about. If it’s a bacterial bloom, it will simply clear up on its own. And if it’s an algae bloom, while it may look unsightly, it won’t have any negative effects on your goldfish.

If you do want to stop the water from being cloudy, just remember the best solution is to follow good cleaning and fish-keeping practices!

And lastly, if you liked this article, make sure you check out the rest of the website! Otherwise, have a great day!

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