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 Water

If you see specks or particles in your water, it is most likely due to fish waste, excess food or dusty substrate. For example, when setting up a new tank or planting aquarium plants, tiny bits of substrate may float into the water column. 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

Till all silt is gone.

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. It is highly recommended that you use an Aquarium Siphon to clean 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. Your filter is like a garbage can for collecting waste, and when it gets full, it can no longer collect particles from the water. To remove the accumulated debris, squeeze the sponge filter or gently wash the filter media in old tank water. 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. Messy fish foods (typically the kinds that contain very few binders) can turn into dusty fish poop that breaks apart very easily in the water. 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.

Keep eartheaters and other bottom feeders in your aquarium as they can stir up the substrate while searching for food on the floor. If your aquarium is constantly cloudy, you might need to add additional mechanical filtration. 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 cannot be reused and should be changed if they get clogged up 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.

Water clarifiers are also available to remove debris-laden water. 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. 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

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. The water looks like someone has poured milk into it. (For more information on beneficial bacteria, see our guide to aquarium nitrogen cycle.

Bacterial blooms often occur when cycling a aquarium or if a big group of fish is suddenly added to the tank because there isn’t enough beneficial bacteria to support the ecosystem yet. 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 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 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.

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. 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 off very little light, so make sure the aquarium is completely blacked out.) You should be careful as your plants could suffer from this lack of light. 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. You don’t need a huge one to treat green water. The UV changes the cell structure of algae, so that it cannot reproduce. Once they’ve been sterilized, you can do multiple water changes over time to remove the green water, and soon enough your water will 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. 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.

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. These methods may not work. You can try chemical filtration, such as activated charcoal in a 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, on the other hand, is reusable and can be “refreshed” with bleach to remove the impurities it collects.

5. Cloudy Aquarium Walls

The problem could be in the aquarium walls. 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. The glare from lights can cause haziness in your aquarium. You can add an aquarium background to the tank’s interior or exterior.

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.