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How to clear a cloudy aquarium tank

Updated July 19, 2017

Several things cause a cloudy aquarium tank. If the aquarium is new or you've recently acquired new fish, for example, the water becomes cloudy due bacterial level adjustments in handling extra waste. Alternately, if your aquarium tank has no new additions and the water becomes cloudy, it requires investigating possible causes to safeguard your fish.

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  1. Collect 1/2 cup of aquarium water to measure the amount of pH, nitrate, nitrite and ammonia in the water.

  2. Perform the tests according to the test kit manufacturer's directions. Read the instructions carefully.

  3. Determine whether there is an excess of ammonia, nitrate or nitrite by comparing the results of the tests with the colour chart that accompanies the test kit. Make sure the pH is stable by checking frequently, especially if your tank is new. A pH that is too alkaline, or above 7.0, makes the water appear cloudy due to the excess dissolved phosphates, silicates or heavy metals.

  4. Add an appropriate water treatment to counteract the problem. For example, an ammonia neutraliser will change ammonia into a non-toxic form. Excess nitrates and nitrites contribute to cloudy water by encouraging algae growth. If nitrates are the problem, then adding a nitrogen removing media to your filter helps.

  5. Change 20 per cent of the aquarium volume. This removes some of the debris and bacteria that cause cloudy water. Do this every day for a week.

  6. Vacuum the gravel with a gravel vacuum to remove debris and excess bacteria. This temporarily clouds the water by stirring up organic material settled in the gravel substrate. Filters then remove the debris.

  7. Get a handful of gravel from an established tank. This gravel contains beneficial bacteria that digest the waste material in the water and reduce the cloudiness. Most fish stores provide this if asked.

  8. Feed the fish only the amount they can eat in 10 minutes. Overfeeding causes bacterial overgrowth, resulting in cloudy water.

  9. Add aquarium salt and water conditioner to the tank. Salt helps fish fight diseases. Water conditioner removes harmful chemicals, like ammonia, chlorine and chloramine.

  10. Avoid overcrowding the tank. Too many fish in a tank stress the fish and overwhelm both the filter and beneficial bacteria.

  11. Tip

    Prevent cloudy water by cleaning the gravel thoroughly at least once a month. Once your water is no longer cloudy, change 20 per cent of the water volume twice a week to keep it clear.

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Things You'll Need

  • Water test kit (pH, ammonia, nitrate, nitrite tests)
  • Gravel vacuum and hose
  • Measuring cup

About the Author

Christine Jonard is a writer/editor who has been published in several textbooks. Since 2003, she has written feature articles for middle and high school biology textbooks, middle school earth sciences and general biology labs. She has copy-edited textbooks through final pages. She has a B.A. in English, a B.S. in zoology and a B.S. in psychology, all from the Ohio State University.

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