Why is My Fish Tank Cloudy?

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Picture this: You have just come home from work, ready to kick back and relax, only to find that your fish tank is full of cloudy water.

If you panicked for five minutes before running to ask Google, “Why is my fish tank cloudy?” you can be assured that cloudy fish tank water won’t kill the inhabitants – so long as you act without delay.

how to get rid of cloudy fish tank water

The thing is, cloudy water rarely develops overnight. It’s best to check in on your tank at least every other day.

There are a few main signs that cloudy water in fish tanks is beginning to form. It could be a grey, cloud-like murk starting to hide your beautiful fish from view, a greenish tinge that is beginning to turn the tank into a swampy mess, or even a yellow-ish brown tinge lowering the clarity of the water.

Now, don’t freak out, because cloudy aquarium water is a minor crisis in most instances. However, there are a few reasons why the water may turn cloudy, and some of them can harm your fish or aquarium equipment if left unattended.

Despite being time to consume, and perhaps a bit costly, these issues are all relatively easy to fix.

Grey Cloudy Fish Tank

A lot of novice fish owners have probably freaked out over their aquarium water turning a cloudy grey.

As unpleasant as it may be to own a tank full of water that looks like thin, rancid milk, grey water isn’t too much of a trouble – most of the time.

Work your way through the list below to narrow down what the problem is.

Gravel Residue

A common mistake for new aquarists, grey water can be a product of gravel residue. This one will become apparent right after you initially fill your tank.

You need to thoroughly wash all of the gravel before placing it within; otherwise, all the fine grit, dust, and dirt coating it will contaminate the water.

Plumes of grey will cloud the water straight away. Larger pips of gravel will sink back down within moments, but the remaining dust will clog up your filter and make life harder on your fish.

The good news is, fixing this problem is simple. Empty out the water and remove the gravel from the tank.

Now wash the gravel thoroughly until the water runs clear; be sure to stick your hand in there and stir everything up so that even the finest pieces of dust are shaken loose.

High Acidity

When introducing new water to a tank, or setting up a tank for the first time, it is vital to treat the water with the appropriate conditioner.

An overabundance of contaminants in the water, or high acidity levels, can cause a cloudiness in the water.

Not only do conditioners remove harmful bacteria from the water, but they reduce the acidity of the water to healthy levels for fish.

All good aquarium shops will carry a range of conditioners, and they should have pH water testers also; grab a few of these to monitor your tank as you condition the water.

cloudy fish tank

Bacteria Colonies

Bacteria colonies are actually good for your tank. They break down waste and help keep the ecosystem stable.

These colonies can bloom into a cloudy mass for a few reasons, and depending on the condition of your tank, one or more could be the cause. Blooms can pop up on day-one or they can arise years down the line.

Introducing new plants, water, or fish to a tank can cause blooming, as foreign bacteria are brought into the tank. This creates a slight instability in the colonies, resulting in a bloom.

In time, these will settle down; however, if they worsen, you may need to perform water changes on a more regular basis.

Excess food left to decay, as well as dying plants, can result in an explosion of the bacteria population. If you see lumps of fuzzy bacteria clinging to plants, or bits of uneaten food, remove them and lessen the amount of food given during feeding times.

It is also important that you do not clean your filter and perform water changes at the same time.

Leave a few days in between these tasks, as the filter is chock full of the bacteria colonies already established in your tank and the new water needs to be exposed to them.

Green Cloudy Fish Tank

Green cloudy water comes from one thing: algae, the bane of many aquarists the world over. It’s a normal growth and to be expected. However, getting on top of algae is hard, and if you allow it to spiral out of control, your fish will suffocate.

When removing algae from a tank, there is no easy fix. If the growth has become out of control, you will have to remove everything from the tank, keeping a large portion of the water, and scrub the slime away by hand.

Depending on the cause of the growth, there are other solutions as well!


Overexposure to sunlight will cause algae growths to explode. If a green fuzz is starting to crawl over the glass and tank decorations, it is time to leap into action!

Look at your tank. How much direct sunlight is it getting? If it is more than a few hours a day, it may need to be moved to a shadier spot.

Do you have a light for your tank? Turn it off. Don’t leave it on all night, and perhaps avoid using it at all if the tank already gets a healthy amount of natural light.

Nutrients, Nitrates, and Phosphates

Algae can bloom if there are too many nutrients, nitrates, and phosphates in the water. Algae will gobble this stuff up and wriggle into every crevice of the tank.

All you can do here is keep up the regular water changes, use conditioners that reduce the phosphate levels, be careful not to over-populate the tank with fish, and remove excess food and dead plant matter from the tank.

cloudy water in fish tank

Yellow or Brown Cloudy Fish Tank Water

There are times when your fish tank, well – kinda appears full of urine. It’s not attractive to see, and yellow water is a sign of an incredibly unhealthy tank.

Brown water, despite looking iffy, isn’t that much of an issue, should it come from tannins.


Sadly, if the water has a yellow coloring and you haven’t performed a water change recently, it may well be a toxic amount of ammonia turning the water cloudy.

High population tanks can be a victim of this. If you don’t clean the filter or do water changes on a regular basis, the ammonia levels will build in the tank.

This turns the water yellow and acidic if left alone, and will hurt or possibly kill your fish.

Regular maintenance on the tank will keep ammonia levels from reaching this point. You can pop a few live plants in there as well, to build a somewhat self-sustaining eco-system.


Of all the reasons behind colored and cloudy water, this is the only harmless one; for some species of fish, it is even beneficial!

Tannins are an organic substance found in bark, wood, and plant tissues. If organic matter is placed in water, such as a piece of decorative driftwood, the tannins will leech into the water and stain it a brown or amber color.

This absolutely does not harm the tank or fish, and some fish like the water clarity to be on this level. A number of species from Africa, for example, are more comfortable in brown-tinged water.

If you find this cloudiness unpleasant, then removing the driftwood and changing out the water will be your only method for clearing things up.

Now, if there is brown water in your tank and there isn’t any organic matter that tannins could be coming from, it might just be an abundance of gunk that needs to be cleaned out.

Preventing Cloudy Water in Fish Tank

Aside from regular cleaning and water changes, there are a few other things which prevent cloudiness from returning to your tank!

Invest in a Good Filter

A good filter is truly your tank’s best friend. They suck all the gunk out of the water and put good stuff back in.

Investing in a good filter will take a chunk of cash. However, down the line, it will save you time, money, and some stress.

External filters are good powerhouses for large and/or high-population tanks, as they can really churn through large volumes of water a day.

Keep a Regular Tank Maintenance Schedule

Tank maintenance doesn’t just mean giving the filter sponge a rinse under the tap once a month.

It means water changes (between 15% – 25% of the total volume of the tank needs to be swapped out for freshwater) once a fortnight, scooping out any uneaten food, and giving the filter a proper cleaning on the regular.

why is my fish tank cloudy

Monitor the Population – Flora and Fauna

This may seem obvious, but the more fish you put in your tank, the more waste you and your filter will have to clean up.

Be careful with how many fish you include. Cool as it may be to have a whole school of fish chilling in your tank, the amount of waste they will produce can lead to issues down the line.

As for living plants, when they die or drop leaves, bacteria will start to bloom. It is important to tend to these plants just as you would a regular garden.

Remove any decaying segments, as well as pick out loose leaves or stems.

Here’s a video showing more information on how to fix a cloudy fish tank.


Fish tanks can turn cloudy for a variety of reasons. Depending on the color, it could mean a water change is needed, a better filter is required, or that the gravel wasn’t cleaned properly.

Whatever the reason, there is a solution above.

Do you have any tips for preventing or dealing with a cloudy fish tank?

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