What causes cloudy aquarium water?

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(Last Updated On: March 12, 2017)

If you just started your aquarium, or recently changed the gravel and are experiencing a grayish discoloration of the aquarium water, don’t panic. The gravel was probably still dirty. The free-floating dirt particles should settle and get trapped in the external filtration fairly quickly.

A light haze after siphoning the gravel is harmless, and is likely caused by the minor disturbance of the substrate. This usually clears up within 24 hours.

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A yellow discoloration or brown tint is typically attributed to high levels of dissolved organic matter. This can cause the pH to drop significantly, posing harm to the health of your aquarium fish.

Green Aquarium Water

The green water that affects visibility, and is often referred to as pea soup, is an algae bloom— free-floating planktonic single-celled algae growing at a rate that turns the water green.

The cause is always the same— too much light and poor water quality. Excessive light can result from the aquarium lighting, as well as intense room lighting and direct sunlight.

Water changes provide very little help in clearing the water. Algae spores are readily available in the water, including most waters used for changes. An algae bloom can become so severe that the content of your aquarium can no longer be seen in the green water.

Some believe that turning off the lights will eliminate the problem, but this is an ineffective solution, and the problem will continue to occur.

Algae will consume oxygen at night during photosynthesis. A severe algae bloom can deplete the tank of oxygen, so adequate oxygenation must be provided during the light off period.

Dying organic matter creates phosphates, so the filter should be rinsed more frequently during an algae bloom, eliminating some of the decaying matter. Vacuuming the gravel will also help.

Also see ‘Green aquarium water – The free-floating algae bloom‘ for more information.

White Cloudy Aquarium Water

White cloudy aquarium water is the result of a bacteria bloom.

Sometimes the cleaning of all the filters at once, or the changing of the gravel can trigger a bacteria bloom, due to the removal of bacterial colonies that have settled on the filter media or substrate. Another cause can be medical treatment of the tank using antibiotics, which may destroy these colonies.

The bacteria are either re-establishing themselves, or crowding the aquarium due to favorable conditions (poor water quality), multiplying at such a high rate that the water becomes cloudy white.

A bacteria bloom is cause for concern:

Bacteria need oxygen. A few grams of bacteria consume about the same amount as an adult human, again posing a threat of de-oxygenation in the aquarium. Immediate action is required if the problem is severe, or persists.

It is also advisable to check on ammonia during the period of a bacteria bloom, as ammonia may rise to dangerous levels.

In a salt-water aquarium, the protein skimmer usually helps to prevent and cure a bacteria bloom, as the bacteria are removed as particles. Make sure the skimmer works properly when a bacteria bloom arises.

A severe bloom can create an oily film and enough foam-depressing agents to make a skimmer go flat (no foam, no function). This has to be taken very seriously. Despite oxygen depletion, ammonia gets more toxic at higher pH levels, which is characteristic for salt-water environments.

It is therefore vital to make the skimmer work again. An oxidation agent such as potassium permanganate can be used. Diluted and used sparingly (1% and only added in the low ml region), it will oxidize enough fat to be picked up by the skimmer, thus jump-starting the system.

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8 thoughts on “What causes cloudy aquarium water?

  1. Asutos Choudhury says:

    I have a 135 US GALLON aquarium tank. Please suggest me fish for keeping. Which fish don’t make the aquarium water cloudy and don’t pollute the aquarium inside. My aquarium size 72 inch (Length) × 18 inch (Width) × 24 inch (Height). Please suggest me some fish.

    • Scott @ Algone
      Scott @ Algone says:

      With a 135 gallon aquarium, you have a lot of freedom to choose the fish you can keep. My suggestion is to visit your local fish store and talk to them about the fish you like.

      As far as cloudy aquarium water is concerned, the key there is not to overcrowd the fish tank. Too many fish will create too much waste, resulting in cloudy water and potential algae outbreaks. Here too, a reputable fish store will able to advise you depending on the species and size of the fish you decide to keep.

  2. Prashant Verma says:

    I have changed fhe full tank water along with panels/gravels alobg with filter cleaning.

    During the next setup of aquarium, I redused the count of gravels in the aquarium. Suddenly, I encountered that my fish start dying all of sudden after 1 week. I added proper Tank Stabilizer in the talk but still 2 fish died in one evening after 7-8 days of water changing and then 2 more by next following morning and evening.

    I tested the water quality after this incident and found that there are very high level of NO2, NO3, GH, KH (pH and CL2 in range).

    Can you please suggest some good tips to reduce above level values quickly and efficiently as it’s causing my fish dying day-by-day which is making me so sad and down.

    Hope to hear some good suggestions soon.


  3. Iris Norton says:

    I have 130 gallon aquarium for my turtle . It’s only filled less than half . I have a 100 gallon filter system on it.
    The tank gets soooooo dirty really guick,( like in three days)
    Water gets brownish , cloudy. What can I do , so don’t have to change water too often or maybe a bigger filter system? Please help

    • Scott @ Algone
      Scott @ Algone says:

      A bigger or additional filter certainly wouldn’t hurt. If you’re changing all of the water each time you are doing a water change, then you likely are disrupting good bacteria needed to break down the waste in the tank. Water changes should be done partially and the filter should not be changed at the same time as good bacteria establish there as well. Please review our guidelines for water changes here and also be sure to use a siphon to remove as much organic waste during each water change as possible. Hope this helps.

  4. Joe says:

    Thanks, I have a marineland filter with two slots. I change both at the same time. I think from now on I’ll change one every other week.

  5. Kate says:

    And it’s true we just bought our two Oranda fish from our local pets at home and we noticed the water was cloudy we found out it was because even though we had washed the gravel we added it after the water unfortunately one of the fish died but that was because of a illness not relating to this. But I would recommend sorting the water out before something happens as they were going to the top of the surface going for air. Thank you

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