How to Clear Cloudy Aquarium Water

Lion fish in blue aquarium water

What is cloudy water?

In short, it’s a bacterial bloom. However it is not the beneficial bacteria normally referred to as nitrifying bacteria. Before those get to work, another set of bacteria is needed. These “scavengers” are heterotrophic bacteria, which feed off organic waste in the fish tank.

This feeding process represents the first stage of the aquarium’s natural nitrogen cycle, at which organic waste is converted into ammonia. The nitrifying bacteria on the other hand continue the process by breaking down ammonia into nitrites, and nitrites into nitrates, completing the nitrogen cycle. Heterotrophic bacteria can double in population every 20 minutes. Its growth depends on available organic waste in the aquarium. In other words, everything that decays in the fish tanks represents a food source for these scavengers. This excessive growth turns the aquarium water cloudy.

How do I clear cloudy aquarium water?

As a first course of action the gravel should be vacuumed using an aquarium siphon. This is where most organic waste accumulates and also where the scavenger bacteria initially grow. If large decorative ornaments are in the fish tank it’s a good idea to move these from time to time in order to vacuum the gravel underneath. The goal is to remove as much accumulated waste from the gravel as possible.

Some other things that will help

  1. Reduce feeding. Most organic waste introduced into the fish tank is from fish food. Overfeeding is common and probably the main cause for cloudy water problems.
  2. Do not perform large water changes. While the intentions may be good, large water changes can severely affect the balance of the aquarium leading to a further deterioration of the water quality.
  3. Consider your fish population. A severely overstocked aquarium will result in excess waste. The general rule of thumb is not to exceed 1 inch of fish per 2 gallons of aquarium water.
  4. Be patient. Taking any or all of the above actions is a step in the right direction. However, the fish tank will need time to balance and recover once favorable conditions are created.

Also see our ‘Aquarium Maintenance and Fish Care Tips‘.

And make sure you check out Algone for clearing cloudy water and removing nitrates and impurities from the aquarium.

Leave a Reply

46 Comment threads
57 Thread replies
Most reacted comment
Hottest comment thread
52 Comment authors
Notify of
Chad G.

I have researched all websites on how to clear a cloudy aquarium. All of their advice is the same, except for the fact that they do not address exactly what it is you’re feeding your fish. Yes, they all say “don’t overfeed your fish”. But the problem may be much more exacting and should also ask “what are you feeding your fish?” I have a nano tank, 6.7 gallons, and problems are much more concentrated in such a small environment. Believe me, I tried everything and then hit on another idea, “is the actual food I feed them contributing to… Read more »

Thank you for your contribution. This is certainly a very important consideration when dealing with cloudy water. The density of fish food will obviously determine how quickly it may contribute to cloudy water. For example, flakes dissolve quickly and will have a much faster impact on water quality issues as it dissolves. The bottom line is to tweak feeding amounts so fish can consume most if it, creating as little waste from uneaten fish food as possible. This combined with an adequate maintenance schedule will help keep overall waste in the aquarium to a minimum, thus help prevent cloudy water… Read more »

Ruth Baldwin

Can I add this to my filter along with the other necessary products?
I have an AquaClear 50 in a 29 gallon tank.
Can I put it to the side or on top of other filters? Foam, carbon and Biomax?

Yes, you can add Algone without the need to remove other media. Either stack the Algone pouch with other media you are running, or simply drop it into the filter box hanging off the back of the aquarium.

Stephanie M

I upgraded my turtle tank from 10 to 20 gallons a couple of days. I filled the tank with about 1/3 his old aquarium water and 2/3 his new aquarium water. His water is a grey cloudy now which I understand is the bacterial bloom. My question is this: we’re having a Rainsoft water filtration and conditioning system installed in our home which will take out all the chlorine, calcium, and other minerals from the tap water. I would like to replace as much of the water in his tank as possible as soon as possible with the filtered water.… Read more »


A water test will give you the best answer. Test for pH and kH and make sure it is suitable for the aquarium.


I have a male flowerhorn about 4 months. Aquarium water slightly turned green. So changing 25% water alternative days. Still the water is not Cristal clear. How many days it takes & Algone is safe for flowerhorn?


Let me re-direct you to the more appropriate article:
Algone is safe to use, no issues. The duration is depending on the overall circumstances (stocking, feeding, maintenance) it can take a few days or a few weeks.

Jackie Ritchie

Hi there I have a 22 litres and 6 neon tetras and 6 Elden guppies, I have had tank for about two weeks and tank was clear and Fish were thriving then the boy in pets at home told me to take 25% water out yesterday which I done and everything was ok and I changed took two artificial plants out and put in a bridge , then by mistake I put a block of blood worms in which was wrong as my neons were getting fatter so I tried to get some out , then I was worried about… Read more »


The aquarium needs to cycle first. This involves bacteria to colonize. Their main function is to keep the environment safe for the fish by converting ammonia to nitrite and nitrite to the less harmful nitrate. Ammonia is created by the fish, but you also helped with the worms. This is a natural process and quite essential for the health of the fish. The cloudiness is the first bacteria to settle, they grow at rates that turn the water cloudy. These bacteria create the ammonia. You likely have ammonia readings, this also stresses the fish and can be the reason why… Read more »


I got my fish tank about 3-4 days ago and left the filter on like instructed. The water was crystal clear and I was proud of my new purchase. I woke this morning to see a white cloudy, murky kind of water. I did dechlorinate it as well PLEASE HELP!!!

No need to panic. The white cloudiness is likely a bacterial bloom. Nitrifying bacteria need to establish in a new aquarium and the water my become a cloudy white in the initial stages. This should clear up on its own. Avoid aggressively large and frequent water changes believing you are solving the problem. This will only lead to a prolonged period of biological imbalance. Slow, incremental changes are key to aquarium success. Feed only once daily, sparingly and don’t overcrowd the aquarium with fish, and things should clear up on its own.


Over tried everything vacuum changing 25 percent of water it a 20 gallon tank I only have 4 fish it been cloudy for 2 weeks now the levels are good I had them checked I’ve changed filter put clear drop water conditioner I’m at a loss help 1st it was an light orange brown color now it’s gray HELP

This sounds like it may be a bacterial bloom since it’s a gray cloudiness. Read more about bacterial blooms in aquariums here.

Also be sure not to overfeed. We recommend feeding your fish no more then once a day, sparingly at that. Most all aquarium problems stem from accumulating organic waste, which comes almost exclusively from fish food.


Hi ,in regards,feeding once a day,,including fry,,living in the same tank,,just once a day?,,,,I have also heard leaving light on too much can make water cloudy,,,true or false?,,,,Thank you.

You can feed fry 2 – 3 times a day. Just make sure you cut down on food per feeding. You shouldn’t need to do this for more then about a week. Also, don’t spot feed. The idea of feeding more frequently is to give fry the opportunity to compete for food, so a little pinch of food in a few different areas of the tank, per feeding, will help distribute the food better and give the fry a better chance to get what they need. Yes, leaving the light on too long can make the aquarium water cloudy. Cloudiness… Read more »

Isabella Winter

Hi, I have had my betta fish for about a month now and his tank has gotten very very foggy. I need help! My bowl is about a 2.5 gallon. I think I might have been over feeding him a little but now I have stopped over feeding him so Idk what to do!

You can change about 15 – 20 percent of water, while siphoning waste from the substrate, every few days to help clear the water. You said you cut back feeding, you might want to consider feeding sparingly only once every other day. A 2.5 gallon aquarium of water will quickly pollute and turn cloudy or experience green water / algae outbreak, compared to a larger tank. Read more about the challenges of small aquariums here.


If your are over feeding him you should add some ghost shrimps. The will eat some of the waste of the fish and the leftovers.😀😀😀


I have been battling cloudy water in the fish tank. It is a 36 gal bow front & was brand new when I got the set up for Christmas. I had been over feeding the fish. About 4 weeks ago I did a 75% water change & changed the filter cartridge & bio media. The water looked great and all levels normal. After a week or so the water started to cloud again so I added water clarifier and it cleared for a few days. Today I did a 30% water change also vacuumed the gravel and the water is… Read more »

Hi Marianne, our general rule of thumb for aquarium maintenance is ‘less is more’. You correctly identified that you were overfeeding, so correcting that was a great first step. I suspect when you changed 75% of the water and also changed the the filter cartridge and bio media, you essentially threw the tank out of balance. This is where less is more. A big change, like you described, will interfere with healthy bacteria growth within the tank. Nitrifying bacteria are needed for a healthy aquarium environment. With your changes, your aquarium likely needed to “cycle” again. In case you’re not… Read more »


I would suggest feeding tiny amount day and night.I have Angels who have paired of now and layed eggs so about 2 years now I’ve had them when I get carried away and fed to much my water always clouds I use 1 and only 1 thing in my tank it’s called Prime everyone who I know that uses it uses it alone with nothing else since I Began using it I haven’t lost a fish.But if I over feed it does cloud my water when it happeneds it always clears up again save your money nothing will clear it… Read more »

lorraine Avallone

Have. 3 Tanks .But Having Cloudy problems with My 70 Gallon . Tried Acurel and still problem still Excisting Please Help.Dont want My Fish to Die

Give Algone a try. Algone balances the aquarium water, removes nitrates, and polishes the water crystal clear. Learn more about Algone here.

Gretel Gonzalez

Hi I forgot to ask I have aquasafe that makes tap water safe for fish it does it have an expiration date but it does have a fishy smell I don’t know if that is normal it’s been awhile, my daughter bys Water Conditioner by Top Fin and we ran out and unfortunately she had a baby and he was a preemie and she is at the hospital with him which is 40 minutes away from here and I had no idea that she ran out of this stuff so I went ahead and ordered from and it will… Read more »


Yes it does have an expiration date, but it is not uncommon for some conditioners to smell. Generally fine to use within 3-5 years. Refer to the manufacturer for details.

Gretel Gonzalez

my fish tank is extremely cloudy In you cannot see through it I just ordered to everything I need to clean it I also ordered a new filter with filters but it will not arrive here till tomorrow and I really need to clean this fish tank I need to know how to do it yourself idea on how I can do it myself or what I can put in there? I would greatly appreciate it I don’t want my fish to die I have one picasimus he is about 5 inches long and I have 2 giant goldfish… Read more »


No matter if you have white or green cloudy water, the reason is always a high nutrient level in the aquarium. There are three main causes for high nutrients levels, tank size in relation to the fish being kept. overfeeding, or limited maintenance. Cloudiness can occur during the initial start up phase (cycle) because excess waste is not processed as efficiently compared to an established tank. It can also occur once the fish matured, and or if aquarium maintenance needs improvement. The best solution is always to correct the problem, without it, cleaning will be temporary and the cloudiness is… Read more »


I have a 10 gallon tank with 8 Molly fish . Everything was going good but recently the water keeps getting cloudy , I have changed filters, water, rocks and added water conditioner as well as clear water . Someone please help me

You should checkout this article about ‘New Tank Syndrome‘. Changing the filters and water, usually has the opposite of the desired effect. Nitrifying bacteria establish in the first weeks of a new aquarium. This bacteria is needed for a healthy tank, because it breaks down organic waste. The waste is almost exclusively from fish food, therefore you must feed responsibly. Our general recommendation is to feed only once daily, sparingly at that. If you are experiencing cloudy water or algae growth, cut feeding to once every-other-day. Fish have a slow metabolism and do not require anywhere near as much food… Read more »

Fish boi

Can bio starter help fix green single cell algae In water

Technically speaking, yes. If it works out in practical terms however is questionable. The introduction of good bacteria into the aquarium should help reduce nutrients such as nitrate, which are a food source for algae growth. However, once the bacteria has been added to the water, the aquarium will re-balance and quickly return to the state in which it is now. So results will be temporary at best. For a more sustained effort eliminating aquarium algae, reduce the amount of waste entering the tank by cutting feeding to once a day (sparingly) and avoid overstocking the tank. Also consider Algone,… Read more »

We remived the fish, from iur 160 gal. Tank for complete cleaning.Took out everything, washed and cleaned entire tank inside and out. Refilled the take and added the Declor and AquaSafe let the water warm to between 75 & 80 degrees at which time we floated the fish for aprox. 30 minutes. Then introdused the fish to the the clean tank. However the water started turning cloudy within a ciuple hours and is still cloudy today ( whats up ?)


You cleaned away the bacteria that make the water safe for the fish. There are several species of bacteria, heterotrophic bacteria break down organic waste, and the beneficial bacteria oxydize waste into ammonia/ nitrite/ nitrate. The bacteria settle anywhere in the aquarium. Cleaning too thoroughly literally wipes them out. Especially the heterothrophic bacteria. These then re-populate the aquarium and that is what turns your water cloudy. You might have enough survivors on the beneficial bacteria, but watch for ammonia.

Here are general tips for maintenance:

Rhonda burbridge

I have 2 Oscars that are about 3 yrs old…one black and one goldfish orange..I have them in a 65 gallon this the right size of tank for their growth?


65 Gallons would be on the very low end having two Oscars. These are big fish and need some room to swim around freely without bumping into walls or tank mates.


I have an aquarium size of 36×18×24 (l×b×h). I have got oscars and 4 tinfoil. These are not so big. The water is cloudy. How do I keep it clear? And I use the food tidbits.


That would be about 65 Gallons … your aquarium is too small for the fish you are keeping. Oscars and tinfoil barbs easily grow to 12-15 inches. Your aquarium will not be able to sustain these fish and more problems are likely to ensue. The best advice is to get a larger aquarium, or more suitable fish for your aquarium.

Susan Groundwater

My water is extremely white and gree cloudy.I have multiple fish and variety. Some are dying. I’ve tried water changes clarifyers nitrate and nitrite mediums but the water has a greenish tint to it now. What can I do to clean the water? I started with well softened water but have used bottled water for changes. At least 20 gallons in a 20 gallon tank. It just gets worse.


Green water is caused by excess waste and influenced by many factors. So is the white discoloration. Overstocking, overfeeding, wrong environment, plants not doing well, substrate, filtration, light, there is an endless list of possibilities. Please contact customer service with more details on your situation.


Hi! I’ve learn so much from the A/Q, thanks! I just set up a 25 gallon planted fresh water tank. Water pH was 8.2 so I used neutral buffer and it become super cloudy. My filter is whisper 30i it has been 2 days and no changes in the water color. What should I do?


PH reducing additives can cloud the water, but the cloudiness will eventually resolve itself. Technically, most plants and fish will adapt to higher pH levels, but it depends on the fish and plants you are keeping. Make sure to test the water you use for water changes to determine the pH of the incoming water. If plants and fish tolerate higher pH, do not fool around with it. If you need to lower the pH, consider and alternate water source, or use peat moss, or driftwood to lower the pH. If the aquarium is new and has not, or is… Read more »


ive just put the water in the tank and its really cloudy from the gravel should i put the filter on to speed up the process.

Yes, run the filter. It’s quite normal for the tank to initially be cloudy due to free floating particles from the gravel.

How long til it clears I did the same think .I washed the rock first ,filled up the 29 gallon, very cloudy .I syphoned about 40%water n rock then added new water .Should it be clear in a few days ?

The aquarium should clear in only a day or two with the filter running. If it doesn’t, the cloudy water is likely not just particles from the substrate.

Click to Hide Advanced Floating Content
Cart Menu Button Image0
Your Cart