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 let you examine the water’s color and cloudiness without interfering.

1. Particles in the Water

The cloudiness in water is usually caused by excess food, fish waste, dirt substrate, and other miscellaneous materials. Small pieces of substrate can float in the water column when you set up a new aquarium or plant your 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

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, don’t forget to clean the filter once every month. The filter acts as a trash can and collects waste. Once it is full, the filter can no longer hold water particles. To remove the accumulated debris, squeeze the sponge filter or gently wash the filter media in old tank water. (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.)

The foods you feed could be the reason your aquarium has murky water. 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, 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. If they perpetually cause cloudiness in your aquarium, you may need to add more mechanical filtration to scrub the water. Mechanical filtration is any type of filtration that physically strains out debris from the water, much like a coffee filter. Hang-on-back, canister, undergravel and sponge filters all help with mechanical filtration. 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.) Power heads can be used to improve water circulation and remove any debris from the aquarium.

Water clarifiers are also available to remove debris-laden water. The water clarifiers contain a special chemical or clay that bonds to suspended debris particles. They cause them to clump together, making it easier for the filter to catch them or to settle on 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. If there is too much nutrients in the water but not enough beneficial bacteria, the bacteria colony will quickly reproduce. 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.)

If there aren’t enough beneficial microbes to sustain the ecosystem, then bacterial blooms may 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 one to two weeks, and the water will gradually clear up on its own as the bacteria reestablishes itself again.

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 provides lots of miniscule food for the fry, while preventing bigger fish from predating on them. Unfortunately, it also prevents you from seeing into your aquarium and can potentially block light from reaching your plants.

Green water is often caused by a combination of too much light and too many nutrients (often coming from excess food, fish waste, and fertilizers). Green water, like bacterial blooms can’t be removed with fine filter floss or huge 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. Be careful with this method because your plants may suffer from the 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 method, we recommend getting a UV sterilizer. Green water is easy to treat so you don’t have to buy a large one. 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.

If you aren’t adding more tannins to your water, manual water changes may be able to slowly remove brown water. If you have a new piece of driftwood, soaking or boiling it can help the tannins leech out more quickly. 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 becomes clogged up with tannins and toxins over time and must be disposed of. 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. 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? Check out our free guide that teaches you what kind of water change schedule is right for your aquarium!