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 enable you to inspect the water’s color and cloudiness more closely without causing any interference.

1. Particles in Water

The cloudiness in water is usually caused by excess food, fish waste, dirt substrate, and other miscellaneous materials. Tiny bits of substrate might float into the water column, for example, when installing a new tank or setting up aquarium plants. Usually, the powder settles or gets collected by the filter after a few days, but if you’re still having issues after a week, you may need to do multiple large water changes or thoroughly

rinse the substrate

Till all silt is gone.

It is important to set a regular maintenance schedule for your aquarium. We highly recommend that you use an aquarium siphon to vacuum the substrate and change out the water. For a step by step guide on how to use an aquarium siphon, see this article.

Also, clean your filter every month. The filter can be compared to a trashcan that collects garbage. It can no longer absorb particles from water if it becomes full. Use a sponge filter to get rid of the accumulation. (Remember that after you clean your tank and filter, the water may remain cloudy for a couple of hours until the filter has a chance to re-gather the floating specks.)

Your aquarium may have murky water despite regular cleaning. The most common cause of murky water is messy fish food (typically those with very few binders). This can lead to fish poop that easily breaks down in the water. Instead, feed “cleaner”, foods such as frozen bloodworms or live foods. These will be gobbled up quickly, and then turn into 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. If they perpetually cause cloudiness in your aquarium, you may need to add more mechanical filtration to scrub the water. Mechanical filtration refers to any type of filter that physically removes debris from water. It is similar to a coffee filter. Mechanical filtration can be achieved using a variety of methods, including undergravel, hang-on-back and sponge filters. For a customized filter, you can use a prefilter sponge to cover your intake tube. To catch larger particles, you can also use a coarse sponge pad and a fine poly pad. Fine poly pads can’t be reused and should always be replaced if they become clogged with gunk. Additionally, you can improve water circulation with power heads to eliminate any dead spots in the aquarium and make sure any loose particles get sucked up by the filter.

Finally, water clarifiers can be used for clearing up water that has become cloudy due to debris. They contain a special clay or chemical that bonds with suspended debris particles, causing them to clump together so that they get caught by the filter more easily or settle to the substrate. Because the water clarifier sticks to the particles to increase its size, oftentimes the cloudiness can look worse before the filter has a chance to gather all the debris.

2. Bacterial Bloom

Now if you’re looking at the tank water in a white cup and it looks like diluted milk (with almost no visible particles), you may be dealing with a bacterial bloom. The bacteria colony reproduces rapidly when there are too many nutrients in the water, but not enough beneficial bacteria. This rapid population growth makes the water look like someone put a spoonful in the tank. (Read our guide to the aquarium nitrogen cycles for more information about beneficial bacteria.

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. It can also occur when a large portion of the beneficial bacteria has been killed or removed. This could be caused by overcleaning of your tank water, changing too often or using medications that aren’t safe for beneficial bacteria.

It is easy to do nothing. You don’t need to add UV sterilizer or change the water often to clear the haziness. This only makes the bacterial bloom more persistent. 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 can also be caused 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 is a great food source for fry and prevents larger fish from preying on them. Unfortunately, it also prevents you from seeing into your aquarium and can potentially block light from 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 not able to be removed with fine filter floss, large water changes or even giant 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 7-10 days, then do another large water changes. Green water can survive on very little light so ensure that the aquarium is fully blacked out. You should be careful as your plants could suffer from this lack of light. Dead algae can also cause an ammonia spike in fish that may harm them or another green water bloom due to the excess nutrients.

Instead of using the blackout technique, we recommend using a UV sterilizer. You don’t need a huge one to treat green water. The UV light actually alters the structure of the algae’s cells so 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

Tannins are an organic compound found in catappa leaves and driftwood. This is why your tank water may have a brownish tint instead of being green or milky-white. 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. If you have a new piece of driftwood, soaking or boiling it can help the tannins leech out more quickly. 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 can be reused and “refreshed with bleach” to get rid of 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. You can clean your main viewing panels with an algae scraper. Next, use an aquarium-safe cleaner to wipe the outside. Make sure to use an acrylic-safe scraper to avoid micro-scratches. 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.

Are you unsure how often your fish tank should be cleaned? Our free guide will show you the best water changing schedule for your aquarium.