5 Ways To Fix A CLOUDY Fish Tank That Actually Work

In Aquariumsby PaulK

Struggling with a cloudy, disgusting fish tank?

Of course you are or you wouldn’t be reading this article.

Now you can have a crystal clear aquarium overnight without starting over.

If you want to learn from the experts on how to fix your cloudy aquarium water, then this short guide is for you. 

But first, you need to understand the root problem…

Bacteria bloom – certain types of bacteria that live on the bottom of your tank feed off the waste material from fish or food or dead organisms. When you have a new fish tank that you’re cycling, the bacteria in your filter has not grown enough to eat the waste going through the filter. That means the bacteria in the tank grows emphatically, known as a bacteria bloom, and makes your water cloudy. This will be a milky white cloud.

Poor filtration – Your filter is not cycling enough water per hour. It could be that filter size is too small for the tank and you need to upgrade. You should have three types of filtration: Biological, Mechanical, and Chemical. It could be clogged filters that need to be cleaned. It’s important to clean or replace your filters regularly (except for the bio-media filter).

Overfeeding your Fish – The food you give your fish has high amounts of protein, so overfeeding them causes waste to build up too fast for the filter to handle.

Dead Fish – You may not notice that you have dead fish or other water life like snails in the fish tank. A dead fish can cause all sorts of problems if not dealt with right away because you will have much more organic material in the water causing the aquarium water to go foul and cloudy.

Poor Circulation – If the water isn’t circulating, dead spots can arise where the aquarium water is not being filtered. Bacteria feed off of the dead spots causing bacteria bloom. Install an aeration pump with an airstone or a wavemaker if it’s a larger tank.

Overcrowding your Tank –  Similar to overfeeding your fish, overcrowding could result in too much waste being produced for the size filter you have. Get another tank to house the excess fish.

Poor water parameters – Too much ammonia or nitrites have built up and is causing the fish tank bacteria to bloom. Always check your water quality with a test kit. Ammonia and nitrites should be close to zero or zero.

Having your tank light on too long – The light for your tank should only be on at the most 8-10 hours per day. Any more and you start to see algae growth.

Milky cloudy is bacteria driven, while green is algae driven. You need to understand the difference in order to get the proper solution.


Steve Poland Aquatics

Tip #1 – Overfilter your tank. If you have a 50-gallon tank, you should be using a filter rated for a 100-gallon tank. The reason is that the flow rate on the box is for the filter without the media. Once you stuff it full of media, the flow rate goes down. You should be turning over the tank 5 times per hour. Read my review on HOB power filter vs Canister.

Tip #2 – Polyfil. Use a coarse foam, then some pinky floss, then polyfil for the fine mechanical filter. Polyfil is cheap and it works great.

Tip #3 – Don’t overfeed your fish. Uneaten fish food is a big contributor to poor water parameters. Especially if you don’t clean your fish tank often.

Tip #4 – Use a good chemical filter like Seachem Purigen to remove any tannins that may be in the water from driftwood etc.

Primetime Aquatics

Tip #1 – Proper fish tank maintenance is key. That means doing water changes and vacuuming out your substrate regularly. This will pull out a lot of the uneaten food and fish waste that could be the primary cause of aquarium water cloudiness.

Tip #2 – Secondly, clean your glass or acrylic tank. It may be that it’s just the glass that’s dirty, looking like a cloudy tank.

Tip #3 – Thirdly, make sure you clean the mechanical filter media. If that gets clogged, it will stop collecting particulates from the water. If you just have a coarse mechanical filter, you will want to add a fine mechanical filter after the coarse filter to catch everything.

Tip #4 – Finally, start underfeeding the fish and if your tank is a bit overstocked,  reduce the number of fish to another tank.


Tip #1 – Add bacteria to the tank to enhance the beneficial bacteria. This will out-compete the nuisance bacteria that may be causing a bacteria bloom.

Tip #2 – Hook up a UV sterilizer. The UV sterilizer will prevent nuisance bacteria from reproducing.

Tip #3 – Use a coagulating agent like Acurel F. This will clump a lot of smaller particulates together, making it easier for your mechanical filter to stop.

Quebec Cichlids

Tip #1 – First you have to protect the fish and get rid of any ammonia or nitrites that may be present. You do this with a product called Seachem Prime. It takes about a week for things to get back to normal, so you have to add some every day for a week.

Tip #2 – Add a bacteria enhancer like Microbe-Lift Special Blend to get the bacteria going again eating the bad stuff. You also should get some ammonia resins like Sea Pora ammonia resin and nitrite/nitrate resin.

Tip #3 – Perform a 10% water change every day until all of the ammonia and nitrites are gone. If you still have some ammonia or nitrites present, you may have to reduce the flow rate on your filtration system to allow the bacteria to grow.

Tazawa Tanks

Tip #1 – Flow and floss in your filtration system. Use a more powerful filter than you need and some type of floss material for mechanical filtering.

Tip #2 – Move your lighting up towards the front of the tank. The color of the light and how bright it is will affect how clear your water looks, so experiment a little. If you’re getting algae, then reduce the amount of time your lights are on per day.

Tip #3 – Clean your glass both inside and out.

Tip #4 – If your water is turning brown, it’s usually because of decaying plant matter producing tannins so remove any excess dead plant matter and clean off any driftwood or other decorations, then use a good chemical filter.

Tip #5 – Frequent water changes. (sound familiar?)

Filters That Will Help Fix a Cloudy Fish Tank

There are three main types of filters that every fish tank should have. Biological filters that grow bacteria to help absorb ammonia and nitrites. Chemical filters that filter chemicals in the water, and Mechanical filters that filter out the solid wastes in the tank that are most likely causing the cloudiness.

The important filter for cloudiness would then be a mechanical filter. Ideally, you want to have 3 stages. First a coarse filter, then medium, then a fine filter. This will catch 99% of the particulates out of the water for maximum water clarity. 

Filter pads would be the easiest solution since they can be cut down to size and come in many porosity levels. The higher the porosity, the smaller the particulates the filter will catch, but will also clog faster.

Filter socks would be the best solution for clear water, but require frequent maintenance and aren’t designed for many types of filters.

Pillow casing, does a very good job. You have to be careful though not to get any that are bleached or dyed as that can be harmful for your fish.

Open-cell polyether filter foam. The advantage is that this can also double as a biological filter.

Quilt batting is 100% polyester. Make sure there are no additives like fire retardants in the material.

Polyester fiberfill, also called filter floss does a fabulous job.

Polyester mesh fabric can be purchased at your local fabric store. There are many different grades and colors available.

Woven plastic filters are not the most effective, but can be used in conjunction with other filters.

Coarse sponges are lower maintenance but don’t do as good a job in clearing the water.

What if I have no fish and my aquarium water gets cloudy?

If you have a new tank with no fish yet, it’s actually normal to get cloudy from a bacteria bloom from new tank syndrome. The bacteria start feeding off of the dead organisms that come from the plant or rocks in the tank and grow so fast you can see them. Once bacteria build on in your filter, the cloudiness should go away. You can add bacteria into the water to speed up the process. Adding a floss filter will also help clear the water faster.

When you do a water change, clean the filter, or clean the gravel, you upset the balance of the tank ecosystem. When that happens bacteria in the tank will blossom and grow until the balance is restored by bacteria growing the filter medium

Remember when you first start a new tank and are cycling the tank, water cloudiness is to be expected. Ride it out and let the good bacteria build in the filter system, then the cloudiness should go away.

If cloudiness persists, then try some of the cures above until your water clears up. If you have green algae check out this article on getting rid of algae in your tank.

Best Canister Filter for 75-gallon tank.

When it comes to fishkeeping, what is your single biggest challenge or frustration? Leave a comment below.

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