How to Clear Up a Cloudy Fish Tank

A cloudy aquarium can make it difficult to enjoy your fish tank. In this article, we explore the many reasons why your aquarium may look hazy and how to clear up the murkiness as quickly as possible.

You will first need to pour some tank water into an empty plastic cup or bucket. This will enable you to inspect the water’s color and cloudiness more closely without causing any interference.

1. Particles in the water

The cloudiness in water is usually caused by excess food, fish waste, dirt substrate, and other miscellaneous materials. For example, when setting up a new tank or planting aquarium plants, tiny bits of substrate may float into the water column. The powder usually settles or is collected by the filter within a few days. However, if the problem persists after a week you might need to make multiple large water changes or thoroughly clean the tank.

Rinse the substrate

until all the silt is washed away.

If the aquarium has not been cleaned in a while, then setting a regular schedule for tank maintenance will help remove the excess waste so that the water remains consistently clean and clear. We highly recommend that you use an aquarium siphon to vacuum the substrate and change out the water. This article will provide a step-by–step guide to how to use a gravel vacuum.

Also, don’t forget to clean the filter once every month. Your filter is like a garbage can for collecting waste, and when it gets full, it can no longer collect particles from the water. Use a sponge filter to get rid of the accumulation. Remember that the water will remain cloudy for several hours after you have cleaned your tank and filter. This is because the filter needs to get rid of any floating particles.

The foods you feed could be the reason your aquarium has murky water. Fish foods that are messy (usually those that have very few binding agents) can cause a lot of fish poop to form in the aquarium. Instead, feed cleaner foods, such as single-ingredient frozen foods like frozen bloodworms, which will be quickly gobbled-up and become more cohesive fish waste.

If you keep eartheaters and other bottom feeders, they tend to stir up the substrate as they search for food at the floor of the aquarium. You may need to add mechanical filtration to clear the aquarium of any cloudiness. Mechanical filtration refers to any type of filter that physically removes debris from water. It is similar to a coffee filter. Hang-on-back, canister, undergravel and sponge filters all help with mechanical filtration. You can add a prefilter sponge on the intake tube to protect it. The coarse sponge pads will catch larger particles. A fine poly pad will trap smaller particles. (Fine poly pads are not reusable and should be replaced when they become clogged with gunk.) You can also improve the water circulation by using power heads to get rid of any dead spots and ensure that any particles are absorbed into the filter.

Lastly, water clarifiers can be used to clear up cloudy water caused by debris. These filters contain a chemical or clay that bonds with suspended particles. This causes them to clump together and get caught more easily by the filter or settle to the substrate. The water clarifier sticks to the particles in order to increase their size. This can make cloudiness look worse than it actually is.

2. Bacterial Bloom

If the tank water looks almost like diluted milk, and there are no visible particles in it, you might have a bacterial bloom. The bacteria colony reproduces rapidly when there are too many nutrients in the water, but not enough beneficial bacteria. This sudden population boom makes the water look like someone poured a spoonful of milk into the tank. (For more information on what is beneficial bacteria, read our guide to the aquarium nitrogen cycle.)

When there isn’t enough beneficial bacteria in the aquarium, or when a large number of fish are added to it suddenly, bacterial blooms can occur. This can also occur if there is a large amount of beneficial bacteria that has been removed or killed.

It is easy to do nothing. Do not add UV sterilizer to the water or make many water changes to get rid of the haziness. This will only prolong the bacterial bloom. Instead, wait for the water to clear up over the next one-two weeks as the bacteria starts to reestablish itself.

3. Green Water

Cloudy water isn’t caused only by bacteria. You may have an algae bloom if your tank water has a green tint or looks like it is full of peas soup. Green water is caused by tiny, free-floating algae and is actually very good for raising baby fish. It provides tiny food for the fry while keeping larger fish away. Unfortunately, it can also block light from reaching plants and prevents you seeing into your aquarium.

Too much light combined with too many nutrients can cause green water. This is commonly caused by excess food, fish waste and fertilizers. Green water, like bacterial blooms can’t be removed with fine filter floss or huge water changes. Some people suggest doing a large water changing, turning off the aquarium lights, covering the tank with a blanket for 7-10 days and then performing another large water change to get rid of the algae. Green water can survive on very little light so ensure that the aquarium is fully blacked out. Be careful with this method because your plants may suffer from the lack of light. The dead algae can cause ammonia spikes that can harm fish and other green water blooms from excess nutrients.

We recommend that you get a UV sterilizer instead of the blackout method. (Green water is fairly easy to treat, so you don’t need to get a very big one.) The UV actually changes the cell structure of the algae so that it can’t reproduce. Once the algae has been sterilized you can perform multiple water changes to remove any remaining green water. Your water will soon be clear again.

4. Brown Water

If your tank water turns a brownish color instead of green, or is milky white, this could be due to tannins, an organic compound that can be found in driftwood and catappa leaves. While tannins can often be used to keep and raise certain species of fish in blackwater environments (e.g., to keep them alive), most people prefer to keep their aquariums filled with clear water.

Manual water changes can help remove brown water gradually over time, as long as you’re not adding any more sources of tannins. The tannins can be removed faster if you have new driftwood. If none of these methods work, you can use chemical filtration such as activated Carbon in a filter bag or carbon pads, Seachem Purigen, or a hang on-back filter. Activated Carbon can build up tannins and toxins over time, so it must be disposed. Purigen, on the other hand, is reusable and can be “refreshed” with bleach to remove the impurities it collects.

5. Cloudy Aquarium Walls

If there is nothing in your white cup of water, it may be due to the aquarium walls. You can clean your main viewing panels with an algae scraper. Next, use an aquarium-safe cleaner to wipe the outside. Acrylic aquariums require a scraper that is safe for acrylic. Finally, the glare caused by lights around your aquarium can sometimes look like haziness, so try adding an aquarium background either on the inside or outside of the tank.

You aren’t sure how often to clean your fish tanks? Get our free guide to help you decide the right water change schedule for your aquarium.