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Cloudy Aquarium Water: Common Causes & Solutions (Guide)

Why do I have cloudy aquarium water and how do I clear it up? This is a question that’s commonly asked, but rarely answered – both the causes and solutions are so variable.

Often times, the water in your aquarium can be crystal clear one day, and cloudy the next. The onset is swift and it’s not always because of something you may or may not have done!

Luckily, there are a few simple steps that any fish keeper can follow to clear up their aquarium water and get it back to pristine condition.

Before you attempt to fix the problem, you need to know exactly what is causing the cloudy water.

Below we will explain a few causes of cloudy aquarium water and exactly how to fix cloudy aquarium water.

Common Causes of Cloudy Aquarium Water

Believe it or not, cloudy water actually comes in various shades and both not only mean different things, but have very different ways of treating them.

White/gray cloudy water and green water are the two most common types you’ll see; any other color is due to far more uncommon and temporary reasons.

There are many reasons that the water in your fish tank could be cloudy.

Below, we have gone into depth about the leading causes of cloudy water:

Poorly Washed Gravel or Sand

If your fish tank was just set up or is fairly new, cloudy water is most likely caused by poorly washed gravel or sand.

We recommend thoroughly washing your gravel before putting it into the tank.

When setting up new tanks, I dump the gravel into a five-gallon bucket, stick a hose to the bottom, and run it till the water turns clear. Make sure to mix up the gravel/sand in the process to make sure all the substrate is being cleaned.

When rinsing remember that material will still tend to collect at the bottom of the bucket. It’s worth emptying and refilling the bucket with substrate to ensure you get as much fine dust out as possible.

Failure to clean your gravel well can cause more problems down the line, so I would suggest just doing it right the first time.

While it’s usually harmless, if the grain sizes get large enough and it sits in the water column long enough, dust in cloudy water can irritate the gills and slime coats of sensitive fish.

The dust will also tend to settle onto plant leaves, blocking light. It will coat other flat surfaces in your aquarium and looks terrible!

Poor Quality Water

Depending on where you get your water, it may contain high levels of dissolved particles.

These may include silicates, heavy metals, phosphates, or dissolved minerals. Sometimes, these particles leach from rocks or decorations in the tank.

The best way to tell if your source water is the problem is to simply take a look.

Fill a glass mason jar with water first thing in the morning (when potential buildup from plumbing has a chance to be seen) and look at it in a brightly lit location.

Aeration from pressurized municipal tap systems is the most common cause of cloudy tap water but dissipates quickly enough.

If the cloudiness persists it’s likely you have mineral buildup, either due to dissolved solids from your plumbing.

Natural water sources like well water and mineral springs are also subject to seasonal changes that may cause cloudy water.

The main issue with mineral deposits is whether it affects the pH of your aquarium or not; mineralization generally leads to alkaline tendencies.

Even when the water clears, the dissolved solids will remain to some extent. If you keep alkaline-loving fish like livebearers or African cichlids, the natural pH is fine. But tetras, barbs, and other acid-loving fish may suffer.


Overfeeding is one of the most common causes of cloudy aquarium water, especially with new fish tank owners.

New aquarium owners often become too eager to feed their fish and end up over doing it. Excess food that is not eaten usually falls to the bottom of the tank and rots.

This rotting food spurs the growth of bacteria, which can give water a cloudy appearance.

As all aquarists know, bacteria are both essential and detrimental to the aquarium ecosystem. Keeping them in balance is a delicate dance and occasionally things will swing one way or another.

Excess Light

It is usually pretty easy to identify if the cloudy water in your aquarium is caused by excess light.

Generally, excess light produces cloudy water that is green in color, caused by an overgrowth of algae in the water column.

An easy fix to this is cutting down on the amount of hours your light is powered on.

Reduce light running times to 6 hours or even less if possible until your green water is under control.

In addition, you should replace the bulbs every six months or so depending on what type of light fixture you are using. As bulbs age, they shift colors which can promote unwanted algae growth.

Many lower end aquarium lighting systems use incandescent bulbs. These bulbs are not only extremely inefficient but they create a warmer color temperature (5000K or less).

While it’s not a bad look, many aquarium plants can’t make much use of it. Algae, however, finds it perfectly usable and can thrive with little competition from live plants.

Fluorescent and LED fixtures with daylight color temperatures (5500-6500K) are cool, efficient, attractive, and allow plants to thrive. Healthy plants are one of the best ways to fix cloudy aquarium water.

They constantly soaking up nutrients from the water column, keeping free floating algae from becoming a nuisance.

Many light bulbs also have a Color Rendering Index (CRI) printed on them. The CRI indicates how accurately the bulb renders a standard selection of colors. We want a CRI of at least 90 for optimal coloration and plant growth!

How To Fix Cloudy Aquarium Water

Once you have identified the possible causes of the cloudy water, you can work on fixing the underlying problem. Five ways to fix cloudy aquarium water are:

1. Do A Large Water Change

Before anything else, the first thing you should try is doing a large water change. Somewhere around 40-50% of the tank volume should be fine.

Remember that large water changes can be stressful to tank inhabitants. When adding new water, match the parameters in terms of pH and temperature as closely as you can.

I like to use a bit of API Stress Coat Water Conditioner as well. It not only dechlorinates but uses Aloe Vera to stimulate the protective slime coat fish use to keep disease-causing and toxic elements at bay.

A lot of the time, cloudy water is the result of by uneaten food or organic compounds. Make sure you use a siphon and get out anything resting on the bottom.

During the water change, take out any rocks and decorations and rinse them under fresh water. You may notice a thin layer of slime caused by bacterial biofilm.

This is another sign that you have excess nutrient buildup and bacteria is the cause of your cloudy aquarium water.

If you suspect that the gravel wasn’t washed thoroughly, it may be painful but you’re better off emptying out the tank and rinsing the gravel again.

Although this can be a lot of work, unwashed gravel will cause cloudy water for months to come if you don’t get it sorted out.

This is by far the most extreme solution but also the most effective. Remember that if you break down your tank entirely, you’ve more or less reset your bacterial and other aquarium cycles.

Even your filter bacteria are going to go through upheaval if you reset your aquarium entirely.

If you have a large number of fish, you’re going to have to be very careful with reintroducing them. It’s best to move them to a separate tank(s) and then slowly reintroduce them to avoid ammonia spikes and possible death.

Also remember that if your cloudy water is caused by free-floating microorganisms (bacteria or green algae), they may simply repopulate.

This means there’s a deeper imbalance somewhere. Nutrients are being retained in the substrate, filtration unit, or elsewhere. Even a dead fish carcass hidden somewhere can contribute to cloudy aquarium water.

2. Use a Water Clarifier or Water Conditioner

After a large water change and a thorough cleaning, you should use a good water clarifier.

I was kind of skeptical about water clarifiers at first; that was, of course, until I actually used one. A good water clarifier can take your tank from cloudy and murky to crystal clear within a matter of hours

Water clarifiers may seem like kind of a gimmick, but the science behind them is actually sound.

They are a flocculant, which means they cause microscopic floating particles to bind together into larger particles.

The larger grains then either settle to the bottom or get captured by the filtration unit. Flocculants work best on tiny organic particles and algae.

They can but don’t always work with bacteria blooms and don’t work on inorganic dust from unwashed gravel or sand. Flocculants are also used by your municipal tap water system in the purification process!

Algicides are another solution specifically for green water algae blooms. You’ll still want to do water changes and control nutrient load but attacking the algae directly is a great way to fix cloudy aquarium water.

Keep in mind that most but not all are plant safe. Tetra’s Algae Control is one proven to be fish and plant safe.

3. Upgrade Your Filter

A strong filter is the cornerstone on any healthy aquarium. Without a good filter, organic compounds (which often cause cloudy water) do not get filtered out of the water column.

At minimum, your filter should turn over the entire tank volume around four times per hour. This means if you have a 20 gallon tank, your filter should process at least 80 gallons per hour.

In addition, it is important to regularly clean the pads in your filter. Dirty pads reduce the flow rate and don’t remove nearly as many particulates.

Another way to fix cloudy aquarium water is to upgrade your filter to something with a bit more power. Traditional hang on the back style filters are classic for good reason.

They are inexpensive, easy to maintain, and for the most part do a great job. But when it comes to sheer capacity, canister filters are by far the best on the market.

They’re powerful, usually silent, discreet, and fully customizable in terms of filter media, thanks to the compartmentalized design.

For cloudy water issues, we want a canister filter capable of using diatomaceous earth as media.

Not every canister filter can use diatomaceous earth because its so fine grade water will tend to flow over it rather than through it.

You’ll want a pressurized canister filter, like the MarineLand Magnum Polishing Internal Canister Filter below!

Because it filters out so much, diatomaceous earth needs changing more frequently than other media. You may need to change it within the week if your cloudy water issues are severe. But fortunately, it’s inexpensive, easy to dispose of, and will leave your water looking as clear as crystal.

Diatomaceous earth isn’t something you need to use constantly, either. Just when you really need to polish your water.

Recommended Product: MarineLand Magnum Polishing Internal Canister Filter

4. Keep Up With Scheduled Maintenance

No matter how much we all hate them, water changes are a necessary part of the hobby. If you have enough time, I would recommend doing water changes of 10-20% once a week.

If you have a busy schedule, every other week is fine but you’ll want to pay extra attention to your water chemistry and feeding schedules. Having live plants also helps keep your system flexible and self-regulating.

These water changes and cleanings help remove toxins that build up in your tank over time. While Ammonia and Nitrite are processed out by beneficial bacteria, Nitrate is not.

As a result, the only way to remove nitrates is through water changes or uptake by live plants. Failing to remove Nitrates can cause health problems in your fish, algae blooms, and cloudy water.

One piece of equipment that makes water changes and routine maintenance A LOT easier is a siphon. Siphons allow you to get to the tough-to-reach spots, such as the gravel and behind rocks. Also, siphons make the process a lot quicker and more thorough.

Dealing with the bucket brigade of operating a traditional siphon hose can get tiresome and make you want to put off those water changes. As someone who owns larger tanks (75+ gallons) I came to dread hauling 5 gallon buckets back and forth.

Now I use the Python No Spill Clean & Fill for my aquarium maintenance. It attaches securely to the faucet and rather than relying on gravity it uses water flow to create a pressurized siphon!

And once you’ve drained as much water as you need, you can adjust the base to fill your aquarium as well! Just remember to match temperatures as closely as possible and to add your dechlorinator to the aquarium before you add fresh tap water.

5. Cut Down On Feedings

The last step to get rid of cloudy aquarium water is cutting down on feedings. Though simple, this step can be very difficult for new aquarium owners.

Watching your fish get excited when you walk into the rooms can be a little too much temptation to feed them!

Contrary to popular belief, fish don’t need to each multiple times a day. If you notice that your aquarium water is looking cloudy, cut down feedings to once a day.

Only give them as much as they can eat in a five minute period. If this doesn’t fix the problem, cut down to feeding every other day.

Another rough rule of thumb (for smaller fish) is to remember that a fish’s stomach is roughly the same as its eye.

Fish can gorge just as well as we can but there’s little reason for overfeeding other than the entertainment value we get from watching them eat. Cut back on their feeding time as much as possible.

If you’re gone for a large portion of the day or you know you have no self-control because you love your fish so much…consider an Automatic Fish Feeder.

They can be used to precisely control not just when but how much food is dispensed.

Lastly, bottom feeders also help fix cloudy water by ensuring leftovers are properly processed through a digestive system rather than directly by bacteria.

Corydoras and loaches are active bottom feeders that are rarely shy about getting their fair share when it’s time to eat.

Ghost and cherry shrimp are attractive, interesting invertebrates that will also happily snatch up leftover flakes from a feeding. Just make sure you have tankmates for them that don’t see them as a meal! 

6.) Get Live Plants

Live aquarium plants are one of the best solutions to fix cloudy water and are beneficial for aquariums in many other ways as well!

As they grow they pull organic and inorganic nutrients from the water column and substrate, binding it into their leaves and roots.

Aquatic plants are the cornerstone of a healthy aquarium ecosystem. Once they become established, you can even do water changes less often as pruning removes nutrients just as effectively as heavy water changes.

 Aquarium plants are more like biological filtration units that happen to be beautiful! Many plant aquarists leave the substrate undisturbed and simply draw off a small amount of water from the top of the aquarium weekly.

Broad leaves plants like Amazon Sword Plants and Banana Plants also create shadow below them, reducing light available to free floating algae.

Free floating plants like Duckweed, Hornwort, and Elodea create even more shade. And with how quickly these plants grow (especially Duckweed), they help soak up nitrates and organics to remove excess nutrients for algae growth.

Just remember that some of these, especially Duckweed, can become pests in their own right!


Cloudy aquarium water is an issue that a lot of new fish tank owners face. Luckily, cloudy water is not only temporary but easily addressed with a little bit of knowledge!

With our six step system above, you should be able to identify to cause and fix your cloudy aquarium water it in no time.

Once you get your aquarium water looking pristine, remember to keep up with weekly maintenance and add a small amount of water clarifier and conditioner occasionally if you start to see your water returning to green or gray.

Cloudy water can sometimes take weeks to get under control but you’ll be a more knowledgeable fishkeeper for the experience!

Jason Roberts
About Jason Roberts
Jason is an aquarium fanatic that has been a fish hobbyist for almost three decades.

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