Why Is My Fish Tank Cloudy – Causes, Colors and How To Fix It

A cloudy fish tank may raise alarm bells for some. We’d all love to have a tank with perfectly clear water to show off our colorful finned friends and their habitat’s aesthetic decor. More importantly, we want to ensure that our beloved fish are safe and healthy.

Freshwater tanks go cloudy for a variety of reasons such as algae and bacterial bloom or residue from substrates and accessories. Many of these factors can be easily overcome with proper tank maintenance, frequent water testing and a little bit of patience.

Read on to learn more about why your tank may be cloudy, what the different cloudiness colors mean, and how to fix and prevent it!

Here’s a TLDR infographic to summarize what we covered!

White or Grayish Cloudiness in Fish Tank

It depends. If caused by dirty substrates, it’s harmless. But cloudiness may indicate unwanted bacterial blooms which can diminish tank oxygen levels.

It’s quite common to find white or grayish clouds in your tank’s water, especially for new aquariums or after cleaning or cycling the water. This may be caused by impurities in the substrates added or by a rapid growth of bacteria in the system.

Residue from New Substrate

If you’ve just gotten a new bag of substrate, it may be the culprit for the white or gray cloudiness in your tank. 

Gravel, sand and crushed coral substrates tend to accumulate dust build-up after being packed and transported to stores. Once added to your tank, the dust plumes up and causes the water to go cloudy.

The best way to prevent this is to thoroughly rinse any substrate before using it. Here are the steps:

1. Pour your substrate into a bucket and fill it with water
2. Run your hand through the mixture several times
3. Pour the dirty water out
4. Repeat the process until the water appears clear

Your substrate should be ready for use after 24 hours of drying.

You may also:

• Do a 50% water change to try to get rid of the dust
• Use a super fine mechanical filter media or polishing pads to trap the impurities
• Leave it be — the tank’s filtration system should clear the dust after a few hours or days

Rapid Growth of Bacteria

New Aquarium

First-time aquarists may be surprised when their brand new tank turns cloudy even without fish in it. This isn’t a cause for concern. In fact, it’s a good sign that healthy bacteria is growing rapidly within your tank, creating a suitable living environment for your fish. 

These microorganisms are important for oxidizing ammonia and nitrite, removing these toxic substances from your tank.

It’ll take about a week or so for the bacteria and microbe growth to stabilize naturally. Leaving your tank to balance itself out in that time should cause the cloudiness to disappear.

Addition of New Fishes

You may find that your tank turns cloudy all of a sudden when increasing your fish population. This is because the addition of new fishes acts as a new source of nutrients and waste for the nitrifying bacteria in your tank. The new additions create an imbalance in the water, causing bacteria to bloom and stabilize it.

This bacterial bloom causes the white and grayish cloudiness in the tank.

 How to fix it:

To avoid this when populating your tank, you should aim to add less than 50% of the current population at a time. 

Let’s say you currently have 6 fishes in your aquarium and want to introduce 6 new ones. You should only introduce 1 or 2 new ones at a time over a span of 4 to 6 weeks.

Rebuilding of Bacteria Colony

Similar to the cloudiness found in new aquariums, your tank water may become discolored if bacterial colonies are rebuilding themselves. This is triggered when your existing colony is eradicated by the chlorine in untreated tap water or by medications like antibiotics.

You should give your tank a few days to restabilize itself, allowing nitrifying bacteria to recolonize the environment.

For prevention, it’s recommended that you use a water conditioner every time you change the water, especially when using tap water. When rinsing and cleaning filter media, use existing tank water instead of tap water to retain healthy bacteria.

Filtration System Breakdown

Cloudiness may also be an indication that there’s a problem with your filters. A low quality filter may not clear off debris and waste too well, causing your water to be dirty. They also don’t do a good job of clearing nitrites and ammonia, which gives bacteria an excess of nutrients to consume. This may lead to bacterial bloom.

Ensure that your filtration system is working properly and replace any faulty or damaged parts. Make sure to keep your filters clean too, as this can affect their effectiveness. Once the system is up and running again, allow the bacterial bloom to run its course.

Green Cloudiness in Fish Tank

It can be. Green cloudiness usually indicates high algae levels, which can compete for oxygen with your fish.

Green discoloration isn’t just unsightly, it’s also an indication of algae bloom in your tank. While algae won’t directly hurt your fish, a high presence of the microorganism can begin to deplete tank oxygen levels. It’s good to resolve or prevent the issue before it begins affecting your fish. 

Algae blooms usually happen when there’s an excessive amount of light or nutrients in the tank.

Excessive Light

Leaving your tank’s light on for too long or exposing it to intense amounts of light causes algae to thrive excessively. This is because the algae cells in your tank, Euglena, produce food for themselves through photosynthesis.

Minimize light usage in your aquarium until the algae levels start to deplete. Ideally, you should only leave your tank light on for 8 to 10 hours a day.

Excessive Nutrients

Algae also thrives off nutrients in the tank, such as nitrates and phosphates. These nutrients build up when:

Use a diatomic or micron filter to get the algae cells out of the water. Alternatively, they can be killed using a UV sterilizer installed in the tank. 

You should also avoid overfeeding and overstocking your fish to keep nitrate and phosphate levels low. Introducing more plants into your tank can help to do this as well.

Brown or Yellowish Cloudiness in Fish Tank

Typically, no. It’s unsightly but it doesn’t affect your fish.

Brown discoloration is typically caused by a harmless organic substance called tannin. This substance is quite abundant in nature, commonly found on tree barks and plants. Tannic acid, a type of tannin, is usually introduced into aquariums by botanicals and driftwood.

Tannins

When dissolved, plants and wooden decor release tannins into the water all the time. Over time, this may turn your water brown if you don’t do regular water changes. 

Your water may also suddenly turn brown if you’ve recently added unsoaked driftwood into your aquarium.

A quick way to know if tannic acid is discoloring your water is to use a test kit. Measure the tank’s pH levels using the kit — the acid may lower the pH slightly.

You can use chemical filters like carbon to get your water crystal clear again.

It’s also good to soak driftwood decor for 3 to 7 days, replacing the water each time it gets murky, before adding it to your tank.

How To Prevent Cloudiness in Fish Tank

Preventing cloudiness is largely about maintaining balance in your tank. You don’t want excessive microorganism blooms, nor do you want to strip off all healthy bacteria colonies. Keeping excess nutrients to a minimum is the key to keeping your bacteria and algae levels in check. 

To do so, you should limit their access to food and light, while keeping your tank water clean. Here are some tips on how to do just that!

Regular Water Changes

To keep your tank well maintained, it’s advisable to do a water change every 1 to 4 weeks. 

When dealing with a cloudy tank, many hobbyists do more regular water changes. You may try 25% to 40% water changes a week, or for nutrient spikes, every other day. Avoid 50% water changes where possible as it may strip your tank of nitrifying bacteria.

Clean The Fish Tank Glass

Sometimes, your aquarium’s glass may be the cause of the tank cloudiness. This is because bacteria and algae may form a biofilm on the glass, diminishing its clarity. It’s best to clean the tank walls at least once a month to keep it clear. 

Maintain Filtration System

You should clean out your filters about once a month, clearing any solid build-up formed on it or its components. For any rinsing, remember to use tank water as you don’t want to remove all the nitrifying bacterial colonies on your filters.

It’s also a good idea to check the manufacturer’s recommended cleaning methods to properly maintain specific filter models.

There’s also a bunch of filters and filter media in the market like the HAILEA Internal Filter BT1000. 

Getting the most effective one for your tank may take some research and trial-and-error. But once you’ve got a good set up going, you’ll be spending less time cleaning up and more time admiring your gorgeous aquatic pets!

Optimize Lighting

Too much light causes algae bloom, which turns your tank water into an unsightly green color. To prevent this, here’s what you can do:

You may also want to avoid using LED lights as it tends to create a dull, hazy look for your tank. T5 fluorescent lights are the preferred choice — try the Glo T5 Lighting System to keep your tank looking bright and lively!

Prevent Overfeeding

Overfeeding results in a build up of uneaten food that releases lots of nitrates and phosphates. 

To prevent the cloudiness from bacterial and algae bloom, you’ll want to reduce organic waste as much as possible. Only feed fish what they’ll consume in about 30 seconds, or 2 to 3 minutes for slow eaters.

Automatic fish feeders like the GEX Food Clock FC-002 are helpful for feeding precise amounts of food at adjustable intervals.

Utilize Fish Tank Cleaners

Many aquarists make use of fish tank cleaners at least once a month to keep their tanks in optimal conditions.