How To Get Crystal Clear Aquarium Water

by Aquarium Scoop | Last Updated: November 28, 2022

Who would not want crystal clear water in their aquarium? Clear water equates to good water quality, healthy fish and plants, and makes your aquarium look vibrant and vivid. 

In this guide you’ll learn:

  • Why Is Your Aquarium Water Cloudy?
  • How To Get Clear Aquarium Water
  • How Can You Prevent Cloudy Water In The Future?
Crystal clear aquarium with lots of green vegetation

Unfortunately, aquarium water can sometimes become cloudy or discolored for numerous reasons like algal blooms (greenish tinge), organic carbon (tea-colored water), bacteria (cloudy water), or inorganic substances and particulates (grey/brown hazy water). 

Most of these are caused by an imbalance in one or two water quality parameters that causes an overgrowth of bacteria and/or algae or an increase in harmful substances that cause discoloration or haziness of the water. To address these issues, it’s important to first understand what’s behind them so you can take effective action. 

Why Is My Aquarium Water Cloudy?

Aquarium water becomes cloudy, hazy, or discolored due to an overabundance or overgrowth of a certain substance in the water. These usually begin when there is some sort of imbalance in the water quality parameters of your tank. Below are some of the usual reasons why aquarium water can become cloudy and factors that affect them.

small, dirty aquarium

  1. New tank syndrome

Either your aquarium is really new or your tank is suffering from “new aquarium syndrome” or “new tank syndrome” which is when there is an imbalance in the nitrogen cycle of your tank. An incomplete cycle causes cloudy water due to excess ammonium (NH3) and organic matter that cannot be broken down effectively due to the lack of nitrifying bacteria in your tank.

This imbalance may be due to the installation of a new media filter or something in your water quality that caused your good (nitrifying) bacteria and other beneficial microorganisms to die off. A sudden rise in pH levels can cause this, for example. Checking that your filter works properly and allowing your tank to naturally find its balance when you first set it up will help in this situation. New tank syndrome should clear out after a couple of weeks.

📚 Read More >> How To Lower pH Levels In Your Aquarium

2. Bacterial blooms

Bacteria and other microbes are always present in aquariums due to the different biological processes going on in your tank. Sometimes, the delicate balance of these bacteria can be thrown off causing one kind to grow out of control. This often causes cloudy water in aquariums. These blooms should resolve themselves in a few days up to a week without any harmful consequences to your fish. However, it’s good to test your aquarium water at this point to check if any water chemistry parameters are off and address them. Often, an increase in the nitrogen concentrations in your tank (ammonia, nitrite, and nitrate) fuels these bacterial blooms.  

Performing a water change (15-20% at a time) helps keep these blooms to a minimum. If your water is extremely cloudy or if it doesn’t resolve after a week, it might be good to perform a partial water change immediately to prevent the bacteria from affecting your fish. It’s also good to check if your filter is working well or if any of your media filters need any replacement. 

3. Algal blooms

Cloudy or green water can be due to algal blooms. Algal blooms are usually due to an increase in phosphate or nitrate concentrations (nutrients) in the water that is needed by algae to thrive. Too much light in addition to these nutrients allow your algae to bloom. The algae naturally present in your water grow in excess due to the abundance of these nutrients causing a green tinge or increased turbidity in your water, making it look cloudy. Algae can also grow on the surfaces of rocks or leaves, and even on the glass of your tank. 

In low levels, algae aren’t harmful to your fish but if they bloom excessively, they can clog the gills of your fish or consume the oxygen in your water quite quickly once the bloom dies off. This causes a drop in your dissolved oxygen that can kill your fish. 

Measure your water quality with a test kit to check which levels are off and act accordingly. More frequent water changes, checking your filter, adding live aquatic plants, and some algae eaters are ways to keep the algae in your tank in check. It may also be useful to check the concentration of silicates in your tank as these nutrients are loved by fast blooming algae.

📚 Read More >> Why Are My Aquarium Plants Turning Brown?

4. Dissolved inorganic substances or particulate substances

Increased turbidity (cloudy or hazy water) can sometimes be caused by too many particulate substances suspended in the water. This can be very fine-grained sand, substrate, or soil that may have been disturbed from the bottom of your tank and resuspended. Check if any plants were dislodged by your fish that caused the substrate to resuspend or if any of your fish have been naughty and digging up your substrate. 

Other very fine-grained particles in the water like clay, perhaps from your tap, may also cause increased turbidity. Filtering your water before using it in your tank through a sponge or cheesecloth can help prevent this.

Certain inorganic substances like phosphates (PO4) and other minerals present in hard water (calcium and magnesium carbonates and sulfates) can also cause cloudy water and leave a chalky residue in your aquarium glass. Peat filters or diluting your water with distilled or reverse osmosis filtered water can help address this issue.

5. Dissolved organic carbon or tannins

Driftwood, peat, and leaf litter (almond and catappa leaves) have natural substances in them called tannins or tannic acid that can leach out in the water and cause a tea-like discoloration. This can sometimes surprise new aquarium owners who install some driftwood in their tanks. The discoloration is not harmful to fish and can sometimes have antibacterial properties. Tannic acid also helps “soften” your aquarium water by reacting with some of the bicarbonate or sulfate substances that cause water hardness. 

📚 Read More >> How To Soften Aquarium Water

Tannins give the water a natural-looking hue. If you prefer colorless aquarium water, refrain from adding these substances in your aquarium or cure them first by soaking in a bucket of water for a while before placing it in your tank. Curing will help leach out most of the tannins in driftwood or peat.

How To Get Crystal Clear Aquarium Water (The Best Way)

  1. Check your water quality 

Checking your water quality using an aquarium water test kit is a good first step to help you figure out the cause of your cloudy water. If your water chemistry levels and other water parameters are okay, then it may be something with your mechanical filtration. Check your filter and filter media to see if anything is amiss or needs replacement.

If your water quality parameters are a bit off, it may also be your filter (particularly biological and/or chemical filtration) so it’s also good to check. In addition, a partial water change should help you restart or improve the water quality in your tank.

  1. Check your filter

If your water starts to become a bit cloudy, check that your filter is still working properly. You may need to clean it out or replace the media in your baskets to make sure that your filter can work effectively in cleaning out the waste from your aquarium water. 

Pay attention to your mechanical filtration if your water quality parameters are okay since it may not be effectively clearing out the fine particles in your water causing it to become cloudy.

Depending on the capacity of your filter, once you check to see if anything is wrong with your filter and address it, it may take a few hours for your water to clear up. If it doesn’t, you should check to see other factors that may be causing your aquarium water to become cloudy.

  1. Perform a water change

After checking your filter, a partial water change (about 15-20% at a time) will help address a few possible causes of a cloudy aquarium by diluting any waste, bacteria, or algae build-up in the water. It will also help throw off or disrupt the optimum water conditions that may have caused a bacterial or algal bloom and help it naturally clear out. 

If you suspect a bloom, monitor your dissolved oxygen levels closely or increase your aeration to make sure the dissolved oxygen levels do not drop after your water change. It’s also good to have a working filter at this point so it can help clear out excess waste should the bloom die off after the water change.

  1. Evaluate your aquarium set up

If the steps above do not work and your water does not clear up or starts to become cloudy again, then you may have to evaluate your aquarium setup. Check if you might have an overstocked aquarium that is causing too much biological load for your filtration system to handle. You may need a bigger tank if you want to keep more fish or at least a more powerful filter.

Check the equipment that monitors your water quality parameters, especially your thermometer and pH meter to make sure that they are accurate. Warmer waters can promote faster algal and bacterial growth. So does excess light, so check that your aquarium lights are not too intense. Wrong pH levels can also promote the growth of unwanted bacteria. Check the quality of the water that you are using in your tank, as it may be the source of your water quality problems. Properly treated tap water free from chlorine, distilled, or reverse osmosis filtered water are good choices for use in an aquarium.

  1. Deep clean your aquarium

It’s also good to plan on deep cleaning your aquarium if you keep getting cloudy water. Your substrate may need a good vacuuming to eliminate all the waste that may be stuck underneath it. Perhaps it’s actually the glass walls of your aquarium that’s a bit cloudy and not your water itself. Make sure to plan the cleaning day well so you can set up a temporary tank for your fish and plants with the proper water quality parameters while you clean the main tank.


How To Prevent Cloudy Water In The Future

Have a good filtration system

The best thing that will help keep your aquarium water crystal clear is an excellent filtration system. For bigger and well-stocked aquariums with lots of plants and inhabitants, a multi-stage filtration system is best (mechanical, biological, and chemical). Make sure that your filter is powerful enough to effectively clean the volume of water you have in your tank. Sometimes, it’s good to get a filter that is a bit more powerful than the capacity you need – you can never really over filter your tank. You just have to monitor the flow rate of your high-capacity filter and make sure it is not too strong for the fish in your tank.

Add aquatic plants

Aquatic plants have a lot of advantages in terms of maintaining the water quality for your tank and keeping it stable. They absorb excess nutrients such as nitrate, nitrite, and ammonium because these help them grow, preventing the build-up of these nutrients that may cause algal or bacterial blooms. They also help keep the pH of your tank stable by helping maintain the levels of dissolved gasses (carbon dioxide and oxygen) as they use up and produce these during photosynthesis. Plants have the added bonus of making your aquarium look livelier as well.

Add algae and detritus eaters in your tank

Algae eaters and detritus eaters such as glass shrimp, Amano shrimp, Siamese Algae Eaters, Nerite Snails, and Otto Cats do great work as tank cleaners. These invertebrates and fish consume excess waste, uneaten food, and overgrown algae in your tank, keeping them in check and helping prevent any bacterial or algae blooms. These critters are a great way to naturally help clean up your aquarium and prevent your water from clouding up. As a bonus, it’s always fun to watch these critters cleaning up as they go about your aquarium. 

Siamese algae eaters like this one are great for keeping tanks clear.
Siamese algae eaters like this one are great for keeping tanks clear.

Clear out uneaten food

It’s always good practice to clear out uneaten food from your tank before they can disintegrate and turn into waste or sink into your substrate or gravel. Floating pellets are easier to spot and fish out. You should have a good estimate of the amount of food that your tank inhabitants will finish so as not to overfeed and avoid uneaten food from adding waste into your tank. This is also economical in the long run. 

Fish food is high in organic matter and protein that can easily disrupt the chemical balance in your tank if left to disintegrate and decompose. This adds extra-biological load into the water that your filtration system and good bacteria may not be able to keep up with.

Expert Tip

You can try to stick to one feeding area in your aquarium so you can easily spot any uneaten food. Keep this area clear from plants or any objects so you can easily clean and fish out uneaten food.

Choose your fish wisely

Some fish are naturally messy. Goldfish and cichlids are voracious and messy eaters that produce a lot of waste. They also tend to dig the substrate causing debris to resuspend and cloud up the water. 

Take care not to overstock your aquarium. An overstocked aquarium has too much biological load from fish waste causing cloudy water if the filter cannot keep up. Keeping bigger and more fish will lead to more waste, so make sure you have a capable filtration system and/or a big tank to help maintain the water quality. A lightly stocked tank with fewer and smaller fish will maintain crystal clear water more easily.

Use activated carbon as a filter media

Activated carbon or activated charcoal is a natural substance that absorbs odors and binds to certain substances in the water helping it clear out. It is negatively charged allowing it to bind to oppositely charged particles in the water, effectively filtering it out. Most filter media cartridges are often equipped with activated carbon but if your aquarium water is cloudy you may want to add some extra in your media basket to help it along.

📚 Read More >> Why Does My Aquarium Stink?

Use a water clarifier

Several chemical clarifying agents are available in specialty pet stores and online that can quickly resolve your cloudy water. These are usually flocculating or chelating agents that can bind to bacteria, algae, or other particulates in the water and cause them to sink or be captured in the filter. This should be treated as a last resort since these agents can also act on the good bacteria and algae in your tank and cause further imbalance. It’s good to check the possible root cause of your cloudy water first and then try to address the problem naturally. Water clarifiers are often temporary fixes. If you do not address the root cause, your water can cloud up again.

Should I do nothing and let nature take its course?

Most of the time, yes, but you have to balance this decision to make sure the cloudy water does not affect the health of your tank inhabitants. If your water does not clear up after a week then you should definitely evaluate taking action and addressing the root cause of your cloudy aquarium water.

Should I change filter media or get a new filter?

You should be careful in changing your mature biological filter media because it can cause the bacterial ecosystem or the biological balance of your tank to reset. This can cause “new tank syndrome” wherein all the beneficial bacteria is cleared out as you replace your filter and there is not enough left in the tank to effectively process waste or help with the nitrogen cycle in your tank. This causes a spike in waste levels such as ammonia and nitrite. 

To prevent this, you can slowly change your filter cartridges by keeping the old one in with the new one in the basket so it can become recolonized. If you are getting a new filter, use your old filter’s media with the new filter so that you already have a good bacterial colony in place to help clean out the water. Either way, take care not to make any sudden changes in your filtration setup to prevent shocking your system.

Should I change the water more often?

Yes, performing more frequent water changes can help keep everything stable while addressing the problem of cloudy water in your aquarium. As opposed to changing a bigger amount of the water in your tank, changing the water more often will help keep the stability and prevent shock to your tank inhabitants. 

A partial water change of 15-20% weekly is a good rule of thumb, increasing up to 25% for bigger or heavily stocked tanks. Bump your water changes to every 5 days instead of every week if you are having problems with cloudy water then observe and adjust accordingly.


How long does it take for cloudy aquarium water to clear?

Depending on the cause of the cloudiness, it can take from a few hours to up to a week or even two weeks for the water to clear. Observe your fish for any signs of illnesses closely after a week to check for adverse effects or perform a partial water change to help things along. 

What happens if your fish tank is cloudy?

A cloudy fish tank signals an imbalance in the delicate ecosystem of your aquarium. It’s usually due to an overgrowth of bacteria or algae in the water. This can lead to other problems such as an increase in the concentrations of ammonia, nitrate, and nitrite levels that are toxic to fish.

Is cloudy water bad for fish?

Yes and no. It depends on the underlying cause of the cloudy water. Usually, if left unchecked and untreated, cloudy water can become bad for fish. Cloudy water usually signals an imbalance in the ecosystem of your aquarium such as an overgrowth of bacteria or algae. This can be bad as it can lead to a rise in the toxin levels in your tank which is bad for your fish.


Getting crystal clear aquarium water and maintaining it is easy once you understand the underlying causes that lead to cloudy water. These are often due to an imbalance in your aquarium’s system such as an overgrowth of bacteria or algae. Preventing it is simple as it is just good husbandry or applying best aquarium keeping practices such as maintaining an efficient filtration system and proper tank stocking. Keeping crystal clear aquarium water will not only benefit the aesthetic of your aquarium but the health of your fish as well.

Further reading

A great overview on water quality:
Water Quality in the Freshwater Aquarium

Forums on getting crystal clear aquarium water:
New 20 Gallon Tank is Foggy
Advice on How To Make Aquarium Water Clear
One Week Nanotank – New Aquarium Syndrome?