Cloudy water in marine aquarium

Ensuring that your saltwater tank is filled with clean and clear water is really important if you want your marine life to thrive. If you wake up one morning and notice that your marine tank has become cloudy, you should troubleshoot the problem and seek a solution right away.

Cloudy fish tank water can be caused by various different things including:

  • Sand being moved around the tank
  • Algae or bacterial bloom
  • Microbubbles in the tank

With so many things that could be causing your saltwater to become cloudy, there's no one-size-fits-all solution. It's important you identify the problem so you can choose the right solution.


1. Powerful re-circulating pump

A common cause of cloudy fish tank water is an overzealous re-circulating pump. When the pump you've installed is too strong for your tank, it can cause some of the sand (and other particles) inside your tank to get caught up in the water current. The suspended particles give the tank water its cloudy appearance.

To test whether this is the problem in your marine tank, take a sample of the saltwater and leave it to settle. If you notice a layer of sediment appears at the base of your container, then it's likely that the sand has been moved by your pump's forceful flow.

To correct this problem, adjust the power of your pump or invest in a more suitable one. Also, check that your powerheads aren't pointing down towards the sand unintentionally. If you create a gentle current in the water, a sandstorm is much less likely to occur!


2. Bacterial Bloom

Bacterial blooms can occur anytime there's a change in the water, but they most commonly occur when you add new fish and critters to your tank. The cloudiness is often white in colour and tends to appear within a week after your new marine life is added but usually settles down on its own within a few days.

It's important that you have some good bacteria in your tank because it helps to convert harmful chemicals like ammonia into digestible nitrates. This cycle is really important for the health of your fish, so, it's often best to leave the bacteria to cycle through your marine tank system naturally. 

Of course, if you notice that the fish in your tank are gasping for air on the surface of the water, then this might be an indication that the bacteria level is becoming a problem. At this point, we'd recommend removing some of the tank water and replacing it with clean saltwater. You could also increase the supply of dissolved oxygen through your air pump. This is a quick and safe way to reverse the cloudiness in your marine tank.

Other reasons a bacteria bloom might occur include:

  • A sudden increase or change in nitrate or ammonia levels
  • The introduction of water containing chemicals or medicines
  • A change in the filter system/medium that you're using

If the cloudiness of the water hasn't changed in several weeks, or if the water becomes increasingly cloudier rather than clearing on its own, then we'd recommend getting in touch with a marine tank specialist for further guidance.


3. Algae Bloom

If you notice that the water in your fish tank has turned green and cloudy, this could be an indication that there's been a sudden spike in algae. Like all plant life, algae thrive wherever there is light, water, and nutrients. While you obviously can't remove water from the equation, you can adjust the levels of light and nutrients to help get the algae bloom under control.

First, take a look at your marine tank and see if you can work out why there's been a sudden spike in algae that's caused the tank to become cloudy. Here are a few common reasons:

  • Your aquarium is exposed to too much light
  • Too much food has been added to the water
  • Your tank is due a water change

Problem - Too much light

Solution: Move your tank out of direct sunlight. Make sure that your artificial lights aren't stronger than necessary, and install a timer so they're not switched on continually. Too much light will encourage the growth of algae, so limiting it can help to prevent future algae blooms and cloudy marine tank water in the future.

Problem - Too much food

Solution: Try not to overfeed your fish. Too much food can create an unnatural amount of phosphate in the water, this will cause algae to develop. Feed your fish small amounts and check whether they're eating it all. Remove any food that's not eaten rather than leaving it in the tank.

Problem - Water needs changing

Solution: Ensure that 15% of your marine tank water is changed on a weekly basis. Algae blooms can occur when nitrates in the water build-up too much. If you're unsure whether the cloudy water in your marine tank is due a change, why not test it with one of our testing kits?

If you can see that the algae is not only made your fish tank water cloudy but has also clung to the glass, you could use one of our algae removal magnets to get rid of it without having to disturb the critters in your tank too much.


4. Microbubbles

Microbubbles are (you guessed it) tiny bubbles that appear in your tank and make the water look cloudy. Some marine tank enthusiasts would argue that microbubbles can be harmful to your fish and coral if they're left untreated for a long time.

Whether you think they're harmful or not, it's best to find the cause of the problem so you can clear your water up and get back to enjoying your marine tank.

Identifying the source of the bubbles

Microbubbles can occur anywhere where the tank water comes into contact with air, usually in the sump or in equipment like the protein skimmer. Start by looking at your equipment to see how well it's functioning; you might be able to spot the source of the problem straight away!


Do you notice the microbubbles coming from the powerhead? Its likely that the water is mixing with air just above the water. This one is easy to fix, simply pop the powerhead under the surface of the water and the bubbles should clear.

If your tank has been running for a while and you suddenly start to notice microbubbles, this could be an indication that something is going wrong in the sump. When the water level in the sump drops below a certain level, it could start to suck air into the water that's returning to the tank, causing a sudden build-up in microbubbles. Check that your sump top-off is working correctly.

Skimmers need to mix air with the water in order to work, but sometimes, microbubbles exit the skimmer and find their way into your display tank. Make sure your skimmer is working as it should be and replace it if necessary. That should fix the problem.

If you're unsure how to treat your cloudy fish tank water, get in touch with the Rock 'N' Critters team! We can help you to identify the problem and get it fixed as soon as possible.

Contact Rock 'N' Critters

Photo from Pixabay

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