How to Fix Cloudy Water in a New Fish Tank?

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You brought home a new fish tank. You have everything ready—gravel, ornaments, plants, filter and two beautiful little fish quietly swimming in a circular vivarium, waiting for their new home.

But only a week goes by, and you see the fish tank water slowly turning cloudy. You scrub the glass rigorously thinking the glass boundaries of the tank have gone dirty. But that does not solve the problem. So you wonder, “How to fix cloudy water in a new fish tank?

To solve the problem, you need to know the reason behind the cloudy appearance. It could be due to a lack of water change. Or maybe you have been overfeeding and there is a lot of uneaten food particles suspended in the water columns. Or worse, maybe the haziness is due to an overgrowth of bacteria or algae?

There are different ways of detecting the reasons and arriving at a solution. Read more to find out!


Causes of Cloudy Water in Fish Tank

Your aquarium water could be cloudy for various reasons. However, some reasons could be pinpointed to find out the solution. After all, no one would like their fish tank to appear cloudy. It just does not look right.

If the water in your fish tank appears grayish, whitish or greenish, it could be due to the following reasons:


1) Gravel Sediments

Say you just filled the tank and within an hour or so, the tank starts to appear cloudy or whitish. The reason behind this could be the new gravel which has not been washed properly. Sediments or unwashed residues detach from the gravel and mix with the water. Result? Cloudiness.


2) Dissolved Nutrients

The water that you freshly added to your new tank may have had a high level of mineral constituents in them, like phosphates, nitrates, silicates, and heavy metals. This happens when you have added water without verifying its source. Tap water may be high in mineral contents and heavy metals.


3) Chlorinated Water And Disinfectants

Tap water may create what is called a “shock” in the system of the aquarium. Shock refers to a sudden dramatic change. Tap water has a high chance of containing chlorine or chloramines, which may wipe out the entire population of good bacteria altogether.

After the system gets used to the shock, a new nitrogen cycle begins, which leads to a population explosion of bacteria. This sudden blast of bacteria can also be the reason behind the persistent cloudiness in your fish tank.  Adding disinfectants will create a similar type of bacterial shock.


4) Bacterial Growth

The time when cloudiness starts to manifest is a crucial factor to determine the reason behind it. If the whitish appearance is observed weeks or months later, the reason could be an overgrowth in bacterial population.

This phenomenon is sometimes referred to as bacterial bloom or blossom, or the “new tank syndrome”.

The situation of bacteria growing in the aquarium is a good thing, as long as they are good bacteria. Why are bacteria good, you ask? The reason is that they help decompose excess food, dead algae, fish excrements and carcasses into harmless nitrites and nitrates.

You can expect them growing peacefully in your biological filter. If there are too many organic detriments in the fish tank, the bacterial population will also grow, resulting in the haziness of the water.

If you want to know how to fix cloudy water in a new fish tank, caused by bacterial overgrowth, you need to keep on reading.


5) Suspended Algae

At times the cloudiness could be green, instead of whitish or grayish. That’s a clear indication of green algae overgrowth. Light is a factor that determines the growth of these microscopic creatures.

Keeping the aquarium lights on for a long time, and subjecting the fish tank to long hours of sunlight could be a few very strong reasons behind a sudden algae bloom. Algae population can also explode when there are excess nutrients in the fish tank.


6) New Filter Media / Starting The Filter After A Long Time

If the filter has been left off for a long time, movement in water slows down. At one point, water becomes static and stagnant. When there is no movement in the water, O2 supply diminishes, which cause large colonies of bacteria to die off, making the water appear cloudy.

Stagnant water is also a breeding ground of worms and algae, which may further add to the hazy appearance of the water.

Changing the filter media suddenly may also create a shock in the system. Filter media is a lair of good bacteria. A sudden and full replacement of the old filter media with a new one will remove all these good bacteria from the water.

Result will be lots of rotten matter floating in the water columns. Incomplete N2 cycles will follow, all adding up to the cloudy appearance.


How To Fix Cloudy Water In A New Fish Tank?


1) Clean The Gravel

In any new tank, cloudiness from gravel is a common problem. There is no reason to be panic-stricken about this. The simplest way to get rid of that unwanted cloudiness is to separate the fish (if you have added fish already), drain the tank, and keep rinsing with new water until the water runs clear.

When water runs clear, you would need to understand that the gravel has been washed clean.

It might be written on the product label “Suitable for Immediate Use” or something similar. Of course, it is written keeping your best interest in mind, but it would be best if you ignore it and wash the gravel.

You can wash the gravel with RO water or old tank water (making sure that the old tank water is not infected with worms or algae, but not pool or tap water. No other cleansing substance would be required. Thorough rinsing would be sufficient.


2) Change The Water

If the cloudiness of your tank is due to water that has been taken from a source high in mineral content, then the problem could be solved very easily. At first pH test the water with test kits that are readily available in pet stores and online. Water high in mineral nutrients should be alkaline.

Simply add water conditioner in the fish tank, and you should see a quick solution to the problem. Or you can change 10-30% of the cloudy water every week, and replace with Reverse Osmosis (RO) water. Next time you fill your tank up or get a new tank, remember to fill it up with RO water.


3) Prevent Bacterial Overgrowth


a) Stop Overfeeding:

Cloudiness in the aquarium due to bacterial overgrowth is really nothing to be worried about. If you had vacuumed the gravel and practiced regular water changes, bacterial overgrowth would not have occurred to begin with.

Any unbalance in this aquatic ecosystem has an underlying reason, and unless you pacify with this deeper problem, the unbalance will remain and recur. What are the main reasons behind a bacterial overgrowth? A poor or irregular water-changing routine and overfeeding are the two main reasons.

Feeding in excess leave uneaten food in the water, which rot, and you can very well expect bacteria to carry out their decomposition process.

How to fix cloudy water in a new fish tank? Well, what you should do to resolve this problem is as clear as day. Feed fish just two or three times a day and in small amounts each time. The amount of each feeding session should be such that all food gets eaten within a few minutes. You should doubly make sure that no uneaten food is left. Uneaten food could be sieved, siphoned, or vacuumed out.


b) Stop Overpopulating:

An aquarium packed with fish and plants could contribute to bacterial bloom. Overpopulation of fish and plants clearly mean there is an ongoing battle for oxygen, food and space in the fish tank. This might cause certain plants and fish to die, forming carcasses rotting away.


c) Change Water:

The importance of regular water change really cannot be emphasized much. Try to change 10-30% water of your aquarium every week. Depending upon the haziness and frequency of its recurrence, you should then opt for 50-70% water change.


d) Clean The Tank:

Fish poop and carcasses of any organism (once alive) in your fish tank including algae, plants, worms, fish, snails, shrimps, or anything that wriggled or swathed, should be located and removed on a regular basis.

Check beneath rocks, under the gravel, within the crevices in the substrate, they could be stuck anywhere. Wherever they are, they have begun to rot beyond your radar of knowledge. Their rotting is adding unwanted things in your aquarium which you absolutely do not want.

Therefore as soon as you locate them, siphon or vacuum the gravel. If it is too hard to clean with these mechanisms, try wearing a glove and remove them.  Gravel washing products are also available for you to try them out.


e) Chemical Methods:

Alternative methods which you could use would be bio-fluids by Fluval. Bio fluids release fast-acting enzymes into the water columns of the fish tank. These enzymes will strip off any organic particles present in the water columns. No organic detriments, means no bacteria!

Slowly the cloudiness in your tank will start disappearing. After treatment and cleaning, it should not take longer than 2-3 days for the cloudiness to disappear.


f) Include Baby Plants:

In new glass tanks, cloudiness is a common problem. This is mainly because of an incomplete nitrogen cycle. Include baby live plants in your aquarium. Once they start to grow you have to understand the nitrogen cycle is complete.

Floating bacterial bloom, which was causing the cloudiness, will soon settle down, and water will also become clearer with time. This takes about 1-3 days in the presence of fish. If fish have not been introduced yet, the nitrogen cycle will take about 3 weeks to complete.


4) Prevent Algae Overgrowth

How will you get rid of the greenish cloudiness? Green haze in aquariums is due to algae overgrowth. Refrain from keeping the fish tank near direct sunlight, like near open windows or in verandahs.

Use algae scrubbers and scrapers to clean the tanks off algae. An effective way to fix cloudy water in a new fish tank is to set a lighting timer. Limit the lighting hours of the fish tank. Equal hours of light and darkness would do good to your aquatic ecosystem.


5) Add A Filter

Adding a good sponge or floss filter in your aquarium will also bring you benefits in removing the unwanted cloudiness in your fish tank. Good quality filters or pads, like Marina Polywool or Fluval, could be chosen. These products, together with Fluval QuickClear, for example, should be effective.

Fluval Quickclear basically imparts ionic charge which helps to clump suspended particles in the water together that get stuck in the fine filter media. You can also add activated carbon filter cartridges or pads in your filter system.

Never turn off a filtration system. If you really need to do it, the maximum time limit you can afford to keep it shut off for, should only be a few hours. They aerate the water and keep the good bacteria alive.


6) Replace Filter Carefully

You would definitely need to change an old filter cartridge or sponge or pad from your filter after a month or so. That’s taken. But when you do decide a replacement, do not throw away the old media just yet.

One of the most effective ways to fix cloudy water in a new fish tank is to introduce the new media while keeping the old media alongside with it. Why?

The old media has a lot of good bacteria in it. If you keep the old media with the new one, at least for a couple of weeks to a month, the bacteria will shift from the old to the new media and colonize. In this way, the aquarium will be free from bacterial shocks. This will prevent any sort of cloudiness to hamper your tank.


7) Clean The Tank Glass

Have you ever wondered that the reason your tank appears to be cloudy could be simply because the glass sheets of your tank are dirty? There are various scrubbers and on-stick-pads available in aquarium stores or online which could be used to remove algae, worms, dust or detriments accumulating over some time, off the glass surface.

Do not forget the exterior side of the glass! Overtime, the outside of the glass sheets may accumulate finger prints, smears, tints and water spots, which may contribute to the aquarium looking cloudy from the outside.

Wash the glass from the outside too with scrubbers and water, and do this regularly. Glass cleaning magnets are other optional mechanisms which can be used to scrub those hard-to-reach corners of the aquarium. They usually come in rectangular models and are every easy to use.

Another product is lens cleaning spray-bottle with microfiber towels that are great for cleaning the exterior sides of the glass.




1. Would cloudiness harm my fish?

Ans: Cloudiness is not an infestation or infection. In fact cloudiness is not the problem. The problem is the underlying cause of the cloudy appearance.

Bacterial overgrowth, suspended algae, dirty water and dirty tank glass sheets might all make the interior of the tank look hazy or unclear.

If bacterial bloom and algae overgrowth are the reasons for your tank cloudiness, then you might spot some fish swimming way up at the water surface and trying to breathe. That’s a bad sign. That’s mainly due to ammonia toxicity and if left untreated could prove to be fatal for your fish population.

In that case, you might either like to remove the fish from that tank and shift them to a hospital or temporary tank, or carry out large water changes, like 50% at once.


2. How can I easily understand the cause behind the cloudiness?

Ans: You need to keep track of the time over which the cloudiness occurred. If the cloudiness occurs within an hour of adding fresh gravel or tap water, it is probably due to the particles shedding off gravel or floating nutrients in the tap water.

If the cloudiness started to appear within a week or weeks or months, it is probably due to bacterial overpopulation. Adding chlorinated water or disinfectants may also cause cloudiness within 2-3 days.


3. How can seeding the aquarium help in making cloudiness disappear?

Ans: Seeding means taking an object, like gravel, or ornament or filter media, from an old tank and introducing it to a fresh, new tank. It is one of the most practical ways to fix cloudy water in a new fish tank.

The reason is very simple. The objects from the old tank all contain a layer of good bacteria on them which soon colonize the new tank. Then you can finally cycle your tank and add plants and fish. If N2 cycles are complete, the chances of the water in the new tank going cloudy or hazy are very less.



Water in a fish tank may go cloudy with time, especially if you do not change the water regularly. Or maybe the fish tank glass has not been cleaned in a long time?

Cloudiness in fish tank water could be due to such harmless reasons as stated above, or something more nefarious could be lurking in the background.

Overfeeding and poor water change cycles add to cloudy water formation. Lack of a filter and excessive doses of light could lead to the formation of algae, which further promotes greenish cloudiness. Nevertheless, cloudiness is a big but common problem in new fish tanks.

Keep your tank clean, change the water regularly, and do not overfeed. Do not give your aquarium sudden “shocks” and keep it away from direct sunlight. Your fish tank would be good to go!

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