Is Cloudy Water Bad for Fish?

Is Cloudy Water Bad for Fish?

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When you have an aquarium, it’s common for it to become cloudy. There are many reasons why this occurs and it’s actually a rite of passage for any fish keeper.

But, if you’re new to the hobby, you may be wondering if cloudy water is bad for fish. In general, it isn’t bad for fish. That said, it will depend on the color and thickness. If the tank less than six months old with a whitish-gray cloudiness or if it’s yellow-brown, this will not hurt your fish.

Is cloudy water bad for fish?

Technically, cloudy water in and of itself isn’t bad for fish. But, the color is going to be a major factor along with how opaque the cloudiness is.

What does it mean when the cloudiness is white or gray?

If your water is somewhat transparent but there’s a thick white or gray haze making everything appear fuzzy, there are a few possible causes. For tanks less than six months old, it’s establishing a nitrogen cycle. This should take care of itself and clear up within a few days. But, it could be from a newly added substrate or bacterial bloom.


A lot of gravel, sand and soil designed for fish tanks often create a cloud of dust or detritus in the water. If you don’t rinse new substrate well, it can make a big cloudy mess inside your aquarium. In most cases, this should clear up on its own.

But, if it continues after several days, perform a partial water change. You could also get a polishing pad to fit inside your filter. This should help remove some of the particles causing the cloudiness.

Bacterial Bloom

In the case of Bacterial Bloom, the whitish-gray cloudiness can be problematic. It’s the one form of a white cloudiness that can become detrimental to your tank. If it remains too long, it can hurt your fish.

Bacterial bloom occurs because heterotrophic bacterium is burgeoning in the tank. Although you can’t see the bacterium individually, as a collective, they appear as a giant swarm of white cloudy water.

This is not the good type of bacteria that processes ammonia. That kind is autotrophic because it feeds on inorganic substances. Bacterial bloom feeds on food and other organic waste. It’s what causes rotting in fish waste that produces dangerous levels of ammonia.

Causes of Bacterial Bloom

You can promote Bacterial Bloom in your tank due to the following:

  • Dead Fish: a dead fish can foul the water if left for too long
  • Over-Cleaning the Filter: if the filter is too clean, it will destroy the beneficial bacteria
  • Overcrowding: too many fish can tax the tank’s ecosystem
  • Overfeeding: uneaten food is often the culprit of most cases of Bacterial Bloom
  • Poor Filtration: the filtration you provide may not be sufficient enough for the tank size and/or the amount of fish

Removing Bacterial Bloom

If Bacterial Bloom occurs and you have no fish in the tank, there’s nothing to do. It simply means the tank is establishing a nitrogen cycle. Eventually, this will clear up. But, if fish are present, it can deplete oxygen and cause an ammonia spike. Heterotrophic bacterium isn’t directly dangerous to fish but what they produce in the tank can be.

This means you should add an air stone or put the power head near the water’s surface to provide some agitation. Monitor the ammonia levels closely every day to see if it lessens. If there’s an increase, you’re going to have to control it by adding a product to remove ammonia.

Another thing to try is controlling how much food you put in the tank at one time. This will prevent uneaten food from building up ammonia. If the problem is still a big issue, perform a 30% to 40% water change every other day to remove organic compounds.

Preventing Bacterial Bloom

However, prevention is always better than the cure. Be sure to perform regular water changes and clean out your filters using aquarium water. Don’t clean your filters too often and only feed fish what they can consume in two minutes or less.

Is green cloudiness bad for fish?

If you notice your aquarium water turning a bright green, there’s no need to panic. This is one of the least harmful colors for fish. It only looks unsightly and is often caused by Algae Bloom. This is a free-floating algae that wanders around.

Causes for Green Cloudiness

There are three main causes for green cloudiness in an aquarium: light, nitrates and/or phosphates. If light is too intense or if they’re left on too long, it can cause your tank to turn green.

Also, if you don’t perform water changes on a regular schedule, nitrates and phosphates can build up and this is what algae thrives on. Algae love this stuff and will make your tank a yucky green, cloudy color.

Removing Green Cloudiness

Controlling the lighting will be the easiest way to rid your tank of the green and keep it away. Ensure your tank isn’t receiving direct sunlight from windows. Natural sun will boost algae growth to undesirable levels. Monitor how much light your tank gets during the day and how much sunlight gets in.

Lights should only run eight to 10 hours per day. Keep the light low in your tank until you are certain the algae are under control. Gradually increase exposure a little at a time. You may want to invest in an aquarium timer if you find it difficult to control manually.

If nitrates and/or phosphates are what’s causing the green hue overtaking your tank, there are a few things you can do to control it. First, make sure you’re not overfeeding your fish. This is the number one cause for high levels of nitrates and phosphates.

Preventing Green Cloudiness

Always remove dead fish the moment you see them along with dead plant material and fish waste. When you have to adjust pH balance, ensure you use a chemical that doesn’t have phosphates. UV sterilizers can also help kill excess algae.

What does it mean when yellow or brown is clouding the tank?

The least toxic color of cloudiness for an aquarium is yellow or brown. This comes from tannins provided by driftwood and other plant matter. This will not hurt or harm any aquatic life inhabiting the tank.

Tannins Are Safe but Unsightly

Tannins are a plant’s defense mechanism to prevent insects from eating it. This isn’t harmful to your fish and you may even have some species that prefer the brackishness. But, it is unsightly and can prevent you from seeing your fish.

Presoak anything that can leach tannins before adding it to the aquarium. Soaking it in a gallon of salinated water for about a week should remove excess tannins. Also, adding a product that provides a little chemical filtration for your tank can prevent tannins from getting out of control.


Although much of the haze that can occur in your tank isn’t particularly harmful to fish, it isn’t the most aesthetic thing to look at. The best way to control it is to keep to a regular maintenance and cleaning schedule.

See Also:

How to Get Rid of Bacterial Bloom in a Saltwater Aquarium

Can Fish Die from Overfeeding

How to Clean Fish Tank Gravel Without a Vacuum