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.

The first thing you need to do is pour some of the tank water into a plastic cup or bucket that is solid white on the inside. This will allow you to examine the color and cloudiness of the water more carefully without interference.

1. Particles in the Water

The water will appear cloudy if it has specks or particles. This is most likely due to excess food, fish waste or dusty substrate. You might find tiny pieces of substrate floating in the water column while setting up an aquarium tank or when planting new plants. 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. To clean the aquarium substrate and change the water, we recommend using an aquarium siphon . You can read this article to learn how to use a gravel vacuum.

Also, clean your filter 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. Keep in mind that water can remain cloudy after cleaning the tank and filter. The filter will then have a chance of re-gathering the floating specks.

The foods you feed could be the reason your aquarium has murky water. It is possible for fish foods with a high amount of binders to become muddy and clumpy. Instead, feed cleaner foods like live foods and single-ingredient frozen foods such as frozen bloodworms. This will help to quickly get eaten up and make more cohesive fish waste.

Keep eartheaters and other bottom feeders in your aquarium as they can stir up the substrate while searching for food on the floor. If they perpetually cause cloudiness in your aquarium, you may need to add more mechanical filtration to scrub the water. Mechanical filtration can be described as any type that physically strains out water debris. This is much like a coffee filters. Mechanical filtration is made possible by the use of sponge, undergravel, and hang-on back filters. If you have a customizable filter, add a prefilter sponge to cover the intake tube, use a coarse sponge pad to catch the larger particles, and get a fine poly pad to trap the smallest particles. (Fine poly pads are not reusable and should be replaced when they become clogged with gunk.) To improve water circulation, power heads can be used to remove dead areas from your aquarium and to ensure that all particles are captured by 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. Water clarifiers stick to the particles to make them larger, so cloudiness can often look worse before the filter can collect all of it.

2. Bacterial Bloom

If the water in the tank looks like diluted milk and you can see almost no particles, it could be a bacterial blossom. A bacterial bloom occurs when the water has too many nutrients and not enough beneficial microbes to eat it all. The sudden increase in population makes the water look as if someone has put a spoonful milk into the tank. (For more information about beneficial bacteria, see our guide to the aquarium nitrogen cycles.)

If there aren’t enough beneficial bacteria, it is common for bacterial blooms to occur. It can also happen if a significant portion of the beneficial bacteria is removed or killed – such as by repeatedly changing large volumes of tank water, overcleaning your filter (especially if it hasn’t been serviced in many months), or using certain medications that are not safe for beneficial bacteria.

Simple answer: Do nothing. Don’t add a UV sterilizer or do lots of water changes to remove the haziness; this just makes the bacterial bloom last even longer. Wait for one to two more weeks before the water clears up. The bacteria will reestablish itself and then the water will naturally clear.

3. Green Water

Cloudy water isn’t caused only by bacteria. An algae bloom is when your tank water turns a dark green color or your aquarium appears to be full of pea soup. The algae bloom is tiny and free-floating and can be very beneficial for raising fish. It provides lots of miniscule food for the fry, while preventing bigger fish from predating on them. It prevents you and your aquarium from being visible, and can possibly block light reaching your plants.

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 is similar to bacterial blooms and cannot be treated with fine filter floss or large water changes. To kill algae, it is recommended to do a large water switch, turn off the aquarium light, wrap a blanket around your tank for 7 to 10 day, then do another large water changes. (Green water can survive without much light, so make certain the aquarium is darkened completely. Your plants might be affected by this method. The dead algae can also create an ammonia surge that could harm the fish, or cause another green water bubble from the excess nutrients.

Instead of using the blackout technique, we recommend using a UV sterilizer. It is relatively easy to treat green water, so it doesn’t make sense to invest in a big one. The UV actually changes the cell structure of the algae so that it can’t reproduce. After sterilization, you can use multiple water changes to get rid of the green water. Soon enough, your water will be clean again.

4. Brown Water

Your tank water can have a brown tint, instead of green or creamy white. This is often due to tannins. Tannins are organic compounds naturally found in catappa and driftwood as well as other botanical materials. Although tanins can be used to breed fish that prefer blackwater environments and are commonly used in keeping them, most people prefer aquariums 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 become clogged with tannins and other toxins and should be disposed off. Purigen, however, can be reused and can be “refreshed” with bleach to remove any impurities.

5. Cloudy Aquarium Walls

If you don’t see anything in your white cup of tank water, it could be the aquarium walls causing the problem. Make sure the main viewing panels are clean by using an algae scraper to scrub the inside. Then, wipe the tank’s exterior with an aquarium-safe cleaner. If you have an acrylic aquarium, make sure you’re using an acrylic-safe scraper that won’t cause micro-scratches everywhere. An aquarium background can be added on either the outside or the inside to help reduce the glare.

Do you not know how often your fish tank needs to be cleaned? Get our free guide to help you decide the right water change schedule for your aquarium.