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Why is My Fish Tank Cloudy? (Simple Reasons & Easy Solutions)

Lindsey Stanton Profile Picture

By Lindsey Stanton

goldfish in dirty unclean tank

Owning and maintaining a fish tank is a fantastic hobby, but it’s also a significant investment, both of money and time, so getting home to see that your fish tank doesn’t have the lovely clear water you’re expecting can feel disheartening!

But don’t panic – cloudy-looking water is a very common issue, and once you’ve worked out what’s causing it, you can go ahead and get started with the simple solutions.

In this article, we answer the question: “Why is my fish tank cloudy?”

We look at the 6 most common causes and problems, then offer advice on how to solve it and get your aquarium back to holding crystal clear water.

But first:


What do People Mean by ‘Clouding?’

The first obstacle to overcome in giving your fish tank a nice clear view again is to make sure you know what people mean by ‘clouding.’

One point many new fish owners may not realize is your water can appear very cloudy one day, and then seem clearer the next. But don’t just ignore it, because if you don’t solve the problem, that cloudiness is sure to come back with a vengeance!

The color of a cloudy tank will start to look cloudy, murky or slightly gray, and in most cases will just look slightly hazy. If you have a more serious problem with cloudy water, though, you may notice it looks very thick, and even to the point of no longer being able to see the back of the tank.

Goldfish swimming in an aquarium that looks algae filled and with cloudy water
Image Credit: Chaikom, Shutterstock

Why Is My Fish Tank Cloudy? What Causes It?

There’s a large range of issues that may cause your water to appear cloudy, including:
  • Too much bacteria in the water (possibly caused by a faulty filter)
  • Chemicals in the water (usually from some form of chemical additive)
  • Too much fish food being put in the tank left uneaten and rotting
  • Gravel or substrate residue
  • Decorations and ornaments producing by-products
  • Waste created by the fish
  • Bacteria bloom or algae bloom

Because of the various factors that can cause this problem, if your tank isn’t new, a good place to start is by giving your it, and all the decorations and filters, a good clean (while taking care to ensure beneficial bacteria are maintained in your filter media!)

If it’s a new tank, you need to let it settle, and should follow careful instructions about how to introduce any new products and fish into your aquarium environment.

In some cases, this may eliminate the problem without having to go through any further steps. If you manage to solve it early on, just pay attention to what you’re putting in the aquarium and how often you clean it out properly to try and stop the cloudiness from returning.

Make Sure Your Filters are Working Properly

Effective filters are essential in maintaining a healthy fish tank, and if your water is cloudy, it could be an indication that they’re no longer working properly.

Mechanical Filters

It’s important to maintain and clean your filters when you clean your tank, to make sure they’re working to the best of their ability. One common issue with mechanical filters is the pad/sponge can become clogged with debris.

You could clean the sponge using tap water, but it’s ill-advised to do so.

To help maintain a good level of healthy bacteria from your tank’s natural cycles, it’s recommended you rinse your filter media during a routine water changing session with old water removed from the tank. This will avoid chemicals in tap water killing the bacteria you want and need.

If you can’t clean your filters sponges or media effectively, you can replace them, but try not to make a habit of doing this in case you disrupt the cycle in your tank.

fish tank filter hose
Image Credit: mariait, Shutterstock

Chemical Filters

If you’re using a filter that requires you to pour granules into it, make sure you’re using the recommended amount, and not over or under filling it.

If you have a filter bag placed directly into your tank, cloudy water may be a clear sign you need to replace it – these bags will normally last for 1-2 months, but this can vary depending on the product and the size of your aquarium.

Biological Filters

If you notice that your biological filter has become clogged, you will need to rinse it and remove and blockages. It is very important to remember not to use clean water when cleaning a biological filter, as this could seriously disrupt the cycle of your tank. Make sure you only use aquarium water to perform this cleaning.

Biological filters have a very long shelf-life, and should only be replaced if you notice it’s damaged or broken.

Solutions for Common Problems Causing Cloudy Water

If you‘ve cleaned your tank and all the filter equipment properly, and you’re still having an issue with cloudy water, try the following solutions.

If you suffer from cloudy water fairly frequently, it might be useful to walk through these one at a time with a delay of a few days to a couple of weeks between, so you can identify which issue is causing the problem in the first place.

Causes Needing Natural Solutions

If you aren’t keen on putting additives in your tank, don’t worry – not all issues that cause clouding need a chemical solution.

So before you start adding extra chemicals, have a look at these common problems that you can easily solve by changing your cleaning and feeding habits!

Problem: Rotting Food Due to Overfeeding Your Fish

Overfeeding your fish means there is likely to be leftover food in the tank. If you have any bacteria or microscopic life in there, this leftover food means they now have a source to feed on, resulting in them multiplying nice and quickly! High levels of bacteria like this can create the cloudy effect in your aquarium.

Overfeeding is one of the main causes of cloudy water because it is the quickest way to create a bacterial or algae bloom, which you can read more about below.


This is by far the easiest issue to solve…simply stop over-feeding your fish! Make sure you’re only providing the recommended amount of food, and remember to miss out feeding on set days if required and suitable for the specific species of fish in your tank.

Image Credit: Kana.Wana, Shutterstock

Problem: Unclean Gravel

If you’ve cleaned your tank using a siphon gravel cleaner, but the water starts to turn cloudy again as soon as you put it in, it’s very likely to be the gravel that’s causing problems.


You’ll need to wash the gravel carefully and thoroughly to solve this issue, as only a very small amount of dirt or debris can seriously cloud up your water.

During cleaning, make sure the water you’re using to cleanse the gravel runs clear before putting it back in the tank.

Problem: Bacterial Bloom

This is a very natural event in any fish tank and is nothing to panic about. As your tank takes on its own cycle, bacteria will inevitably develop and reproduce.

A key way to tell if this is the cause of your issue is the timing of the cloudiness. Unlike problems with gravel, the water won’t change straight away. Instead, it may be weeks or even months after adding new gravel or decorations to your tank.


If you think bacterial bloom is the cause of your problem, have a go at the following steps to try and solve it:

  • Regular cleaning should start to clear up your water quickly, but do make sure all the filters are clear and working properly during your clean.
  • Feed your fish less: this is the most common cause of problems in a tank.
  • Add a natural water clarifier: if your filter system is working properly, adding a natural water clarifier can be great. The job of this sort of product is to clump together any bacteria or debris in the water to help make sure the filters can remove it.

Problem: Algae Bloom

The big difference between an algae bloom and the other common issues covered here is rather than a cloudy white color being present, if you’re dealing with an algae bloom, you’re more likely to notice a green or even brown tint in your tank.


An algae bloom is a very fast development of algae within a tank, and there are a few things you can do that help to stop the algae explosion process:

  • Feed your fish less: as we have mentioned before, this is a big issue as leftover food will feed algae and bacteria.
  • Perform a large water change: even changing 50% of the water could solve the problem for you.
  • Make a darker environment: algae thrives in the sunlight, so a simple change of position could slow down the growth.
  • Reduce the number of lit hours: if you’re using artificial lighting, this should be on for no more than 10-12 hours per day, so you may need to make sure the lights are turned off more, or consider lower output bulbs.
  • UV Sterilizers: some owners swear by this method as a means to killing off algae and stopping it from re-appearing.
  • Add live plants: this is a great natural solution to the problem of algae growth because live plants will compete with any algae for the nutrients in the water needed to grow, meaning the algae has less chance of survival, effectively being starved.
  • Chemical resolution: there are chemical products widely available to help reduce algae growth. However, these aren’t commonly recommended, as they can do damage to living plants if any are present in the tank. So sometimes they are a great solution, but we’d prefer other natural means first.
Cardinal tetras swim with Amazon sword aquatic plants Echinodorus bleheri_Cheng Wei_shutterstock
Image Credit: Cheng Wei, Shutterstock


Issues Needing Chemical Solutions

If none of the natural solutions seem to be working for you – and we do recommend trying those first – and your water is still clouding up, there are a few causes can be tackled by adding chemicals to your water, or changing those that you would normally use.

Problem: Constituents Dissolving in Your Water

If you’ve cleaned your gravel, but the water is still clouding relatively quickly, a common cause is there may be too many constituents such as silicates and phosphates in the water.


If you think this may be the cause of your problem, you should be able to test your water and notice a high PH reading, meaning you can solve the issue by adding a specialist conditioner to your water.

Another option is to start using reverse osmosis water (or RO water) which you can buy at most good aquatic stores.

Problem: Lack of Aquarium Salt in Fresh Water

This one is a bit more complex and no strong evidence has clearly linked the use of aquarium salt to clearing cloudy water, but lots of fish owners swear by adding aquarium salt to a freshwater tank if they’re having any issues.

The basic principles behind adding the salt are it can reduce osmotic pressure, and also reduce nitrate uptake, so can, therefore, help your fish stay healthier and less stressed.

However, before you decide to go down this route, make sure you speak to your vet or specialist at your local aquatic store to make sure your particular fish will tolerate the addition of aquarium salt to their environment.

fish divider


If you’re ever in any doubt about the health of your fish or of the effect any cleaning or additives to the water may have on them, always remember to speak to your vet or fish specialist before taking action. If you’re happy your fish are healthy, then it’s time to tackle that cloudy water issue!

The best way to deal with cloudy tank water is to try to prevent it from happening in the first place, rather than waiting for it to occur and then searching for a solution. A few good routine practices can go a long way toward this.

Make sure you’re not overfeeding your fish and ensure any gravel or substrate is cleaned very thoroughly before you place it in your aquarium.

And during cleaning, remember to maintain your filters to keep them working efficiently for as long as possible. Proper maintenance doesn’t take much time and will save you having to replace parts or filter media on a regular basis.

If you’re facing a bacterial bloom, remember it’s a very natural stage in a tank’s cycle, so just take the steps suggested to try and help the water return to a clearer state as soon as possible.

Happy fish keeping!

Featured Image Credit: Chaikom, Shutterstock

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