Cloudy Fish Tank Water Causes and Solutions: How to Fix or Clear a Cloudy Aquarium

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On the fishkeeping forums everywhere, I come across loads of people asking about their cloudy fish tanks. “Help! Cloudy water in fish tank, fish dying!” seems to be the consistent cry across many of these sites, and it’s really sad to read about.

A murky fish tank seems innocent enough until the first little finned buddy goes belly up and you know you’ve got to do something fast before the rest follow.

So, to help with the issue, I’ve compiled as much information as I could to answer the whys and wherefores and what to-dos to save your aquarium from the dreaded cloud.

cloudy fish tank water causes and solutions

Why Is My Fish Tank Cloudy? Causes Of Cloudy Aquarium Water

We’ll go in-depth on the causes and solutions below, but if you’re asking why your fish tank water is cloudy, you’ll want to read this quick breakdown of the most common reasons cloudy fish tanks happen:

  • Improperly cleaned new gravel, sand, or other types of substrate
  • Dissolved constituents – like silicates, heavy metals, phosphates, et cetera
  • Bacterial bloom
  • Algae bloom
  • Too much light
  • Overfeeding
  • Excess nutrients
  • Phosphates
  • Nitrites
  • Overstocking
  • Driftwood leaching tannins

The Causes of Milky Aquarium Water: White or Grayish Water

Several of these issues are primarily at fault in new aquarium set ups, but some are the cause of cloudy fish tank water in established tanks as well.

Problem #1: Gravel or Substrate Residue

If your aquarium is brand new or you’ve recently changed your substrate, and you’ve asked “why is my fish tank cloudy after one day?”, the chances are that milky cloud in the aquarium water is due to improperly cleaned gravel substrate.

When you start a new fish tank environment, there are a lot of issues with introducing any item to the water, unless you do so very carefully. The gravel is one of the biggest culprits on what makes a fish tank cloudy.

Solution: Proper Cleansing of the Substrate

Probably the most common cloudy water in fish tank solutions is this one, so let’s hope this is your issue.

Generally, this kind of issue will clear itself up pretty naturally on its own, unless it’s extremely dirty gravel. In most cases, doing absolutely nothing will be the fastest way to clear up the cloudiness. You may want to vacuum the gravel as well, using a gravel vacuum.

Problem #2: Dissolved Constituents

If washing your gravel thoroughly doesn’t resolve the issue of the cloudy water clearing up, then the next most likely problem of new aquarium cloudy water is likely to be undissolved constituents in said water.

These can be silicates, phosphates, or heavy metals, to name a few.

Solution: Testing and Proper Water Changes

Grab your testing kit to see what it says. You’ll likely find the pH is too high – i.e. the tank is too alkaline – and this means you’ll need to treat the water.

There are multiple water conditioner options available, which you’ll need as you keep your aquarium anyway, so be sure to invest in high-quality options that come highly recommended by other aquarists.

Problem #3: Bacterial Bloom

If your new aquarium isn’t cloudy right away, but a white or gray cloud starts to rise within a few days or weeks – sometimes even months – you’re likely dealing with a bacterial bloom of some kind.

This happens a lot with new hobbyists as the new aquarium goes through its initial break-in cycle. This can result in hazy water all the way to milky white water.

Since it takes several months to establish beneficial bacteria colonies – one reason I recommend using live sand to kick-start the process – that can help to clear the waste from your aquarium without your constant attention. And eventually this cloudiness does resolve itself in most cases.

Solution: Keep an Eye Out and Keep Things Clean

Since eventually this cloudy aquarium water situation will likely resolve itself on its own once the healthy bacteria colonies are established, you only have a few key things to do.

  • Keep the aquarium very clean. Remove all uneaten food, decaying plants, or anything else immediately.
  • Vacuum the gravel regularly.
  • Perform partial water changes regularly.
  • Cut back on feeding to reduce excess food decay.
  • Use flocculant to clear away debris that you can’t remove by vacuuming and water changes. These are usually marketed as water clarifiers.

The Causes of Green Aquarium Water: Green to Brown Water

Of course, not all cloud appears right away when you set up a new aquarium. You may find murky fish tank water instead, which can seem scarier for your fish.

Problem #4: Algae Bloom

Pretty much everyone’s heard of algae issues for aquariums. The plant-like organisms grow all over the decorations, glass, rocks, and other objects inside the aquarium, as well as the inside of the glass.

Algae thrives on the same stuff your live plants do: light and nitrogen. If you’ve got an issue with algae bloom in your fish tank, it’s probably due to one of these two issues.

Solution: Water and Feeding Practices Change

You’ll want to change the water out of the aquarium – all of it – using the proper procedures for removing fish, plants, et cetera. You’ll need to do a thorough cleaning of the tank as well as understand whatever caused the issue.

Problem #5: Too Much Light

Though it may seem counterintuitive since you work hard to give your plants and fish as close to real daylight lighting, your aquarium should never receive direct sunlight as it can cause various issues in your tank, specifically a nitrogen spike.

Big reef aquarium panorama

Solution: Change the Lights and/or Move the Fish Tank Location

If your aquarium is currently in a location that receives direct sunlight at any point of the day, you will want to consider moving it. The extra sunlight will cause the algae to bloom and continue to do so, no matter how much you clean and treat the levels in the aquarium water. Instead, move your fish tank to a location that’s in the shade – a corner or the center of a room is great for this.

If your aquarium isn’t in direct sunlight, you should look into your lighting setup. Try reducing the light in increments to avoid to the opposite issue of not providing enough light for your fish tank. Study up on the types of lights and how much you should have for your specific plants and fish. 

Problem #6: Overfeeding

Algae bloom can also come from overfeeding. This issue is problematic for your fish – many have sensitive swim bladders or other biological sensitivities – but it’s also a problem for the whole ecosystem. The extra food rots and releases ammonia and nitrites, which feeds algae.

Solution: Change Your Feeding Patterns

Most species of fish can handle going a day or two without feeding – some for longer – which is helpful for better understanding how often and when to feed your fish. The time of day that you feed them is up to you, but the number of times and how much is critical for avoiding excess food waste in your aquarium. 

There are a few things you can do to work on this issue.

Feed on a Schedule

Most fish do well with being fed only once or twice per day. Be sure to study how many times a day the species you keep should be fed, and then determine exactly when you should feed them each day.

Base the feeding time around your schedule to make sure you’re able to maintain it. For example, if you work at night, set the feeding schedule for when you come home from work.

Feed Them the Right Amount of Food

You’ll want to check for any specifics for your fish species, but the general rule of thumb for the amount of food to give to your fish should be either approximately as much as is the same size as the fish’s eyeball or what your fish can eat within 30 seconds to two minutes.

Feed Them the Right Types of Food

A lot of the fish food on the market isn’t actually a very healthy choice for your fish.

Things made with corn, wheat, soy, or other cereal grains should be given at minimum rather than as a primary source, because they cause health issues. They also cause excess waste which then causes the issues in your tank.

Remove Uneaten Food Immediately

Watch your fish eat, and then immediately remove any excess food that isn’t eaten. This will also help you best understand how much your fish should be fed.

If, for example, your goldfish eats three pellets in the 30 seconds and the fourth consistently goes to waste, reduce the number of pellets down to three. You’ll save money and cleaning time.

use a gravel vacuum to clear a cloudy fish tank
A good gravel vacuum can come in handy when cleaning up excess food particles.

Add in Some Invertebrates to Your Tank

Scavenging fish scrounge through the excess food and waste in the tank and can help reduce some of the issues in the tank caused by overfeeding.

Have Only One Person Do the Feedings

One of the most common issues I’ve found with overfeeding is that multiple family members want to participate in the feedings. The solution to this either assign only one person as “feeder” or allow the kids to take turns.

For example, Bobby feeds the fish every Tuesday and Thursday, Janet feeds them on Wednesday and Friday, and you do the remainder of the feedings. Whatever works for your family is fine, as long as you prevent people from doing additional feedings.

Problem #7: Excess Nutrients

Nutrients like phosphates and nitrates can cause algae and other problematic issues to blossom in your tank. While nitrates aren’t as potent as ammonia or phosphates, they will eventually affect the health of your fish – and will definitely cause issues with your algae battle.

You can detect nitrates easily with a simple test.

Solution: Test and Change the Water

To find the right balance in your fish tank, you’ll have to test the nitrate levels in your tank with the proper testing kit. Nitrates are invisible and odorless, so the testing kit is vital.

Do a water change to remove the nitrates and retest the water. The change will give some immediate relief, but you’ll need to keep battling these levels until they’re cleared out.

Replace your filter media with nitrate-absorbing media and anaerobic denitrifying biofilters to remove the dissolved nitrates in the water. The combination will help reduce and prevent nitrate build-in, but keep up the testing on a regular basis.

Problem #8: Phosphates

Phosphates come from two primary sources: the decaying matter in the tank and the water source itself.

Solution: Get a RO Water System

While it’s certainly not a cheap solution, if you find that your phosphate levels are high, you’ll need to switch over to using a RO system to remove the nutrients from the water.

Reduce the excess feedings as well to drop the phosphate levels.

Problem #9: Overstocking

Gathering a ton of beautiful fish is an exciting idea. The bright oranges of clownfish, the sparkling yellows of angelfish, and the zingy purples of the Royal Gramma Fish all seem like a great idea – all at once, in one place.

But unfortunately, overstocking your fish tank can cause a number of issues. Of course, the behavioral issues like stress and personality clashes start. But the aquarium water conditions also change and deteriorate into a toxic environment. This means, cloudy tank.

Your aquarium is a miniature ecosystem, like a lake or pond. The microorganisms in your aquarium break down the waste, and the filtration system serves to cleanse the water. But just like a lake can only support so much aquatic life, a fish tank is limited. Your fish tank is a closed ecosystem, which means it more easily gets out whack.

busy aquarium with too many fish causing cloudy water

Solution: Reduce Your Stock

But instead of over-filtering and going with too many plants, you should reduce your stock instead. It’s hard to let any of your fish go, but unfortunately, for the best life for your fish and aquarium, you need fewer fish in there.

You can either get another aquarium and start a new system, or you can re-home some of your fish.

Problem #10: Driftwood Leaching Tannins

Certain decorations actually leach into the water. Driftwood is notorious for this with leaching tannins into the aquarium.

Driftwood looks amazing and many different types of fish can benefit from nibbling or rasping on it. But the driftwood can drop the pH levels in your tank a little bit. This can be great if you need to drop the levels in your hard water, but otherwise, this can cause issues.

You may well notice your aquarium water start to turn a yellowish tea color. Often this is because the driftwood that most sellers have available is the African Mopani, which leaches tannins into the water.

The tannins aren’t likely to actually harm your fish, but it can definitely make the color of your water kind of murky and less attractive.

Solution: Boil or Soak the Driftwood

If your driftwood piece is small enough, you can boil the wood to work the tannins out of it. If the wood is too large to boil, then you can place it into a large container and soak it for several days.

This can help draw the tannins out before you place it in your aquarium. Just be sure to only use a container that doesn’t have chemicals or detergents. And only use purified water for either the soaking or the boiling.

After you’ve soaked or boiled the driftwood, be sure to use carbon filters to reduce the leaching. Also have regular water changes until the driftwood eventually stops leaching color into the water.

Problem #11: Ammonia Build-Up

Finally, the last main thing that’s the possible answer as to why do fish tanks get cloudy is an ammonia build up.

Ammonia poisoning is one of the biggest killers of pet fish. Typically, this happens in a new tank setup rather than in established tanks, but it’s not impossible in this situation, either.

Ammonia build-up happens when too many new fish are introduced into a tank at once, when a filter fails, or if the bacteria colonies in your aquarium die off for any reason – usually due to a sudden change in the water conditions.

Elevated ammonia isn’t visible to the human eye, so it’s important to keep an eye on the levels via a testing kit.

Solution: Use a Chemical pH Control Product

The quickest way to deal with an ammonia build-up is through the use a chemical pH control product. These will neutralize the ammonia in the tank.

You’ll need to restrict feedings to drop waste build-up, as well, which is one of the primary causes of ammonia build-up. If the ammonia levels are extremely high, drop off feedings all together for several days until the levels are back in balance.

Also, never add new fish during an ammonia spike. The high levels can cause a loss of your fish.

You can prevent ammonia poisoning, you can get a cup of gravel from a healthy, established aquarium – ask a fellow aquarist buddy – or buy some live sand that will help you establish your beneficial bacteria colonies for healthy aquariums.

Do not wash the gravel and put it into the aquarium you’re starting. Cover it with at least 2-inches of new substrate, and fill the tank with aged, purified water. The good bacteria will help the nitrogen cycle in your tank in less than three weeks. Only add a few fish initially and wait until the tank has fully cycled before you add more.

Avoiding overfeeding and removing excess waste immediately also helps reduce and prevent ammonia issues. Clean the tank weekly otherwise, and remove any dead plants or debris as soon as possible, while doing a partial water change every other week or as recommended for your given fish species.

Test the water for ammonia at least twice a month for early detection.

Is Cloudy Fish Tank Water Dangerous to My Fish?

A cloudy fish tank is not an automatic death sentence for your fish.

A lot of times the algae problems are what cause the discoloration and cloudiness, which means it’s not good for your aquatic life, but won’t always lead to fatal issues.

Cloudy water does become dangerous if there’s ammonia build-up causing it, though, so be sure to check those levels before anything else. Without cycling your tank properly, your fish can definitely die from ammonia toxicity. The nitrogen cycle is what grows the good bacteria in your aquarium, and that bacteria eats the ammonia that fish produce through their waste.

If possible, it’s best to avoid cycling your tank with the fish still in it, though, as a lot of times that cycle can be dangerous for them. The reason is that the massive and sudden water changes are usually to difficult for their sensitive systems to handle all at once.

Can You Just Let Nature Take Its Course?

In many cases, cloudy fish tank water will clear itself up. And doing nothing may well be your best bet on getting the aquarium water clear and fresh fairly soon. You’ll especially want to do this if you notice that your fish tank cloudy after water changes have happened.

There are a few reasons to first let nature take its course – unless you’ve got fish that are dying.

Cleaning your filter or water does nothing but disrupt the beneficial bacteria in your aquarium. And these bacteria are what naturally clean your tank for you and resolve the milky water situation.

Changing out the water only temporarily fixes the cloudiness in the fish tank. Whatever the source is, it’s likely to actually get worse if you change the water because the new water provides more nutrients for the cloud to feed off of.

Finally, cycling is the process of the bacteria in the tank adjusting the environment of the aquarium, which will naturally kill off the source of the cloudiness, unless it’s much more serious than murky water typically indicates.

How to Clear a Cloudy Fish Tank

Above you’ve seen a number of solutions on how to get rid of cloudy fish tank water. Let’s take a look at how to stop cloudy water in fish tank from happening again in the future.

Add in Live Plants, Live Rocks, and/or Live Sand or Gravel

If your tank is pretty new, the issue is likely that you don’t have enough good bacteria growing in your aquarium environment.

One of the best ways to improve this is by adding in live sand, live rock, and/or live plants. These all provide good bacteria that will compete with the bacteria that’s feeding off the other elements in your aquarium and causing that cloudiness.

Live plants also consume ammonia, which is a huge deal for the health of your fish.

Change the Aquarium’s Location

Sometimes the location of the aquarium is the issue and the reason you’ll ask “why is my fish tank foggy?” The reason for this is the light factor. If your aquarium is in direct sunlight, you’ll often find that you get an algae bloom that causes foggy or even murky water.

Technically, the solution is simple: move the aquarium out of the sunlight.

The actual process can be challenging, however. You’ll find some great tutorials on the process that can help you keep your aquarium alive and thriving through it all.

Things You Shouldn’t Do While You Wait and Watch

Do Not Change or Clean Your Filtration

The first big mistake people tend to make when trying to resolve this issue of why is my fish tank cloudy, is cleaning out the filter or replacing the media.

Doing so removes the good bacteria in your system, which means the bad bacteria can grow.

Do Not Change Your Water Completely or More Often

While you wait to see what happens, you may be tempted to change out your water. Don’t do this! A lot of times this cloudy water in a new aquarium is what’s called “New Tank Syndrome” and will clear itself up. Changing the water out will just start the issues all over again.

Instead maintain a regular water replacement.

solution to a cloudy aquarium

How to Prevent Cloudy Water in Future

The primary thing I’d recommend for prevention of future outbreaks of cloudiness in the aquarium is consistently cleaning your tank. This should only be done after the tank is fully established and thriving, though.

You need to have great filtration, keep the pH and other levels balanced properly, keep the lighting just right, and all of that, but without consistent cleaning, none of that will matter.

  1. Use a gravel vacuum and clean the gravel or other substrate every time you do a water change. Usually, this means about 1/3 of the gravel is cleaned.
  2. Clean any algae or other build-up on air stones, filters, glass sides, or any other surface. Do this not by using soap and tap water, but by using a little of the siphoned-out aquarium water for cleaning any objects outside the aquarium – think air stones, decorations, et cetera that can easily be removed and replaced. Rinse with purified water only.
  3. Test the water and verify levels are balanced after the cleaning. Make any adjustments as needed.

You can also switch out the type of filter media you use. You’ll want activated carbon media or filter pads to help reduce algae bloom.

Finally, you should also consistently test your aquarium water to make sure everything is in balance. Make adjustments as needed.

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