Why Is My Saltwater Tank Cloudy? (And How To Fix It)

There is nothing more frustrating than having cloudy water in your saltwater tank. I can’t stand it. If you are going to keep a saltwater tank as a showpiece in your home, then you want the water to be as crystal clear as possible.

why is my aquarium water cloudy?

But it’s not always possible to have pristine looking crystal clear water 100% of the time. Not only is cloudy water ugly to look at, but it can lead to health problems with fish and other livestock in the tank.


Let’s look at the reasons why you might have cloudy aquarium water and what you can do to fix it.


What causes a saltwater tank to be cloudy?


There are many reasons why a saltwater aquarium might have cloudy water. The main causes being microbubbles, sand being blown around, bacterial blooms, algae blooms, dirty filters and equipment, lack of water changes, fish spawning, and calcium precipitation.


Microbubbles can easily cause aquarium water to be cloudy. Most times it can be caused from a protein skimmer that has not been set properly or hasn’t been broken in yet. This can take time and it’s normal for microbubbles to be produced into the tank.




Also if you are using a sump system, the return pump can also produce microbubbles that can flow into the display tank. For the most part, microbubbles in the tank are not harmful but can be very unsightly. If you are seeing a large number of microbubbles, it can really cloud the water and cause it to look hazy which is difficult to see through. The nice thing about microbubbles is it’s easy to fix.

Protein skimmers do an amazing job of aerating the water. But unless you have it set up properly, you will see huge amounts of these microbubbles. So setting up the skimmer correctly will eliminate this problem and over time as the skimmer adjusts to your tank and gets dialed in, the microbubbles will be reduced.

One of the best protein skimmers that produces very little microbubbles is the Bubble Magus Curve 5. Read my review of this skimmer here.


bubble magus curve a5 review


If you are using sand as a substrate in your tank, you know how easy it can be for sand to be blown around. This is usually caused by wavemakers or powerheads being too strong and the flow is causing the sand to be stirred up. This will almost always cause cloudy water.

It’s important to have the proper amount of water movement in your tank. Blowing sand around is not a good idea, it can cause many problems including cloudy water.

Another issue with sand is when you add new sand to the tank, you will get cloudy water. No matter how many times you rinse it prior to adding to the tank, your water will still be cloudy. Some sands are better than others with respect to clouding your water, but it is inevitable and you will get cloudy water from adding new sand.

This will go away over a period of a few hours to a day or so.

Bacteria blooms are very common with newer saltwater tanks. Setting up a new tank requires a lot of patience and time for the tank to properly cycle. During this time it is common to see bacteria in the tank to rapidly reproduce causing a milky white cloudiness to the water.

This bacteria feeds off of waste in the tank and over time as your tank matures and finishes the cycle, the cloudiness will improve. 


Saltwater nitrogen cycle


Algae blooms are another cause of cloudy water. They differ from bacteria blooms where the water will turn green with an algae bloom. This can be caused by many reasons. Excess nutrients in your water, too might light, can be causes.

If your aquarium is placed near a window, it may be getting to much natural light causing an algae bloom. This is a very common mistake and you should not place your tank near a window. I have had this happen to me and the algae blooms can be so bad that your water turns completely green where you can’t see through it. This can also be very bad for fish and others in the tank.



Dirty filters and other pieces of equipment can cause cloudy water. All equipment requires maintenance and this includes cleaning and replacing filter cartridges, foam pads, biomedia, and anything else you filter your tank with. Over time these items become clogged and dirty losing their effectiveness.

In order for any equipment to perform at it’s optimum, it must be maintained properly. If not, your water will not be as clean resulting in cloudy water.


We all know how important performing water changes are in a saltwater tank. Without water changes, you most likely will see cloudy water. A great way to keep your water looking as pristine as possible is to perform regular water changes on a schedule. Not only will water changes improve the overall health of your tank, but it will help keep the tank looking great.


Another reason why you might have cloudy water is that your fish or corals may be spawning. Usually spawning is a sign of a healthy tank and seeing your fish spawn is exciting. But the downside to that is it’s possible this could lead to cloudy water. Fish eggs can sometimes release a white milky substance which causes cloudy water. 

 Marine Depot Aquarium Supplies


If you notice your saltwater tank is getting very cloudy, another possible culprit could be calcium precipitation. This is very common and it’s often seen on equipment like powerheads and filters. Calcium precipitation can cause particulates to be suspended in the water column causing the water to be cloudy.

Normally caused by the addition of too much calcium supplement or Kalkwasser mix. Also if your alkalinity level becomes too high, calcium levels will drop causing precipitation and a fluctuation in PH. It’s important to test your water levels on a consistent basis and make sure not to add excess calcium into your tank.  


How to clear a cloudy saltwater tank – treatments


The method used to treat a cloudy saltwater tank will depend on the reason why your tank water is cloudy to begin with. For the most part, cloudy water will go away on its own and you will just need to be patient. If you are cycling a new tank, this is normal and cloudy water will improve over time.

If you are dealing with an algae bloom, you can perform a water change and invest in an aquarium UV sterilizer. These are an affordable way to eliminate free-floating organisms like parasites, algae spores, and bacteria that can be harmful to your tank.

For a bacterial bloom, a water change is your best option. Also, consider fewer feedings and don’t add any new fish until the bloom is taken care of. Check your filters and equipment and make sure they are cleaned and performing properly.

If you are dealing with calcium precipitation, find out what was added to the tank to cause it. Did you recently add excessive lime water to the tank? If so this will go away over time. Check the PH of the tank and if it’s too high, consider lowering it as this will help eliminate existing precipitates of calcium carbonate.


How long does it take for cloudy saltwater aquarium water to clear?


It depends. I know that’s not what you want to hear but it really depends on the reason why the tank is cloudy. Sometimes all it takes is a water change and the tank is clear right away and other times it can take a few days. If your tank is new and going through the cycle, it can take 4-6 weeks for it to clear.


More tips on how to keep your saltwater tank crystal clear


Keeping the water in your tank clear can be a hassle. It’s important to perform routine maintenance on your tank to keep it looking it’s best. Here are a few more tips.

  • Perform regular water changes
  • Keep the sandbed clean
  • Use a protein skimmer
  • Use a UV sterilizer
  • Use a sump system or refugium
  • Use a good algae glass cleaner like the Flipper (which I highly recommend)
  • Use activated carbon and filter floss




A cloudy saltwater tank is very common and can be frustrating. But once you know what the cause is, you can easily eliminate and prevent it from happening again. Like everything in the saltwater hobby, patience is going to be key with cloudy water and routine maintenance will go a long way in preventing it from happening in the first place.