Cloudy water in a new fish Tank?

One of the most common aquarium owner questions and complaints for new fish owners is on the topic of cloudy or milky aquarium water. What does it mean? Why does it happen? And how can I fix it?

The good news is that cloudy water isn’t necessarily an emergency situation. In fact, there are some very simple ways to diagnose and treat your cloudy fish tank water and each will be walked through below.

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Why Is My New Fish Tank Water Cloudy?

Does your brand new aquarium suddenly have cloudy water after being clear for the first few days? Don’t worry. A newly set up aquarium is a biological blank slate, there are virtually no life forms present. A variety of microscopic organisms are all trying to establish themselves in the tank. The nitrifying bacteria that filter the water and create stability and balance haven’t had a chance to colonize the system yet, so it’s kind of a free-for-all for a week or so. Free-floating bacteria and other microbes take advantage of minerals and nutrients in the water and begin to multiply unchecked – thus causing the cloudiness. The situation is sometimes compounded and exacerbated when hobbyists add too many fish all at once and/or feed too much, providing these microbes with an additional food source.

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The Best Solutions for Cloudy Aquarium Water

A natural reaction is to “do something”.  There is obviously something “wrong” with the tank, requiring action on our part. However, prevention/avoidance is far better than attempting to mitigate cloudy water once it starts. When you begin to see cloudy aquarium water, it’s best to do nothing and let it run its course, but continue reading for some additional insight.

Should I do nothing and let nature take its course?

  • Yes! Without question, doing nothing is the best approach for a new fish tank. Cleaning the filter does nothing except disrupt the few beneficial bacteria that have had a chance to get established. These “good guys” will eventually outcompete the cloudy water bacteria for food, starving them out and breaking down their carcasses.
  • Water changes clear the water temporarily, but in a day or two the cloudiness reappears, often even worse than before. That’s because the new water provided a fresh supply of nutrients, causing the cloudy water bacteria to populate even more.
  • Left alone, the cloudy water bacteria will eventually consume all the nutrients in the water and die out. This is cycling!

Should I add live plants or other beneficial bacteria?

  • Yes! Live plants have “good” bacteria and other microbes on them, which help initiate the biological balance in the aquarium.  
  • Live plants compete for nutrients and help starve out microbes that cause cloudy water.  In addition, they produce oxygen during the day, which aids in the breakdown of fish waste, uneaten food, and the cloudy water bacteria as they begin to die off.  This third benefit helps clear the water.  
  • They also consume ammonia generated by fish and uneaten food, which tends to build up in newly set up aquariums until the nitrifying bacteria become established.

Should I add or change filtration?

  • No! The big thing in terms of the filter when dealing with “New Tank Syndrome” cloudy water is don’t mess with it. 
  • Cleaning a brand new filter or replacing the pad does nothing good, and potentially eliminates the good bacteria that are trying to get established. If the filter pad or media are in need of cleaning sooner than the first 30 days, you are overfeeding, overstocking, or both.

Should I change the water more often?

No! Regular partial water changes (at least 25% monthly) are the #1 thing aquarists should do to be successful, EXCEPT during new tank syndrome. As mentioned above, the water clears temporarily (24 hours at best), but the cloudiness comes back with a vengeance because you just gave it a boost of nutrients with the incoming water.  


How to Prevent Cloudy Fish Tank Water

1. Do not overfeed your fish

Beginning aquarists often fear their fish will starve to death, so they feed heavily and often.  Unfortunately, there are few, if any, nitrifying bacteria present to break down the resulting waste or uneaten food, which the cloudy water bacteria take advantage of and continue to multiply. Even worse, harmful ammonia and nitrite levels may begin to rise. Fish in nature don’t always eat every day, and some predatory fish may only eat once or twice a week. No fish ever starved to death in three days.

2. Don’t put too many fish in your fish tank.

More fish mean more waste and more food for the microbes causing the cloudy water. Too many fish in your fish tank may also cause a rise in harmful ammonia and nitrites.

3. Add activated carbon media to the filter, whether loose or carbon pads. 

Adding activated carbon media or activated carbon pads to the filter will help clear the water and adsorb nutrients that feed the bacteria bloom.

4. Seed the aquarium.

If you have access to another healthy, well-established fish tank, adding a few handfuls of gravel from that aquarium will seed the beneficial bacteria and speed up the clearing process. Aquatic stores sometimes keep filter cartridges, bio-sponges and wheels floating in stocked aquariums to seed them with bacteria. Then, they could send these items home with new setups to help get the biological balance going. This is the same effect as adding gravel from an established tank.  

5. Test your aquarium water. 

Have aquarium water tested for ammonia and nitrite as soon as the water begins to get cloudy. In most situations the levels will be zero, meaning there is no cause for concern. 

We understand that seeing cloudy water in a new aquarium, can be alarming. But the best advice is to be patient and wait it out. Don’t add any more fish, feed sparingly once every other day, and just leave the filter alone for the time being. 

Cloudy water in an established aquarium is another issue. 

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