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.

First, pour the tank water into a cup or bucket that’s solid white inside. This will enable you to inspect the water’s color and cloudiness more closely without causing any interference.

1. Particles in the water

If you see specks or particles in your water, it is most likely due to fish waste, excess food or dusty substrate. Small pieces of substrate can float in the water column when you set up a new aquarium or plant your plants. Most of the time, the powder settles by the filter and gets collected by it after a few days. If you still have problems after a week, multiple large water changes may be necessary or thorough cleaning.

Rinse the substrate

Until all silt has been washed away.

Setting a schedule for aquarium maintenance is a good idea if the aquarium hasn’t been cleaned in awhile. This will allow the water to remain 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, 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 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.

Your aquarium may have murky water despite regular cleaning. 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, try to feed “cleaner” foods – such as live foods or single-ingredient, frozen foods like frozen bloodworms – that will get gobbled up quickly and turn into more cohesive fish waste.

Eartheaters and bottom feeders can cause algae to build up in aquariums. You may need to add mechanical filtration to clear the aquarium of any cloudiness. Any type of water filtration that strains out the debris, such as a coffee filter, is called mechanical filtration. Hang-on-back, canister, undergravel and sponge filters all help with mechanical filtration. 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. Power heads can be used to improve water circulation and remove any debris from the aquarium.

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. If there is too much nutrients in the water but not enough beneficial bacteria, the bacteria colony will quickly reproduce. This rapid population growth makes the water look like someone put a spoonful in the tank. (For more information on beneficial bacteria, see our guide to aquarium nitrogen cycle.

If there aren’t enough beneficial microbes to sustain the ecosystem, then bacterial blooms may 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.

The solution is simple: 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. 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 is a great food source for fry and prevents larger fish from preying on them. 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. Like bacterial blooms, green water cannot be removed by fine filter floss or giant water changes. Since algae requires photosynthesis to make food, some people recommend doing a large water change, turning off the aquarium light, wrapping a blanket around the tank for 7 to 10 days, and then doing another large water change afterwards to take out the dead algae. Green water can survive on very little light so ensure that the aquarium is fully blacked out. This method can cause damage to your plants. Also, the dead algae can create an ammonia spike that harms the fish or causes another green water bloom from the excess nutrients.

Instead of using the blackout technique, we recommend using a UV sterilizer. (Green water is fairly easy to treat, so you don’t need to get a very big one.) The UV light actually alters the structure of the algae’s cells so 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

When your tank water has a brown tinge instead of green or milky white, it’s often caused by tannins – an organic compound naturally found in catappa leaves, driftwood, and other botanical materials. Tannins are often used to keep and breed certain fish that prefer blackwater environments, but most people prefer to keep aquariums with crystal clear water.

If you aren’t adding more tannins to your water, manual water changes may be able to slowly remove brown water. The tannins can be removed faster if you have new driftwood. If these approaches still don’t work, try using chemical filtration – such as activated carbon in a filter bag, carbon pads, or Seachem Purigen – in a hang-on-back or canister filter. Activated Carbon can build up tannins and toxins over time, so it must be disposed. 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. Acrylic aquariums require a scraper that is safe for acrylic. A background aquarium on the outside or inside of your tank can help to reduce glare and blurred vision.

Not sure how often you need to clean your fish tank? Get our free guide to help you decide the right water change schedule for your aquarium.