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Clearing Cloudy Water – Common Aquarium Questions

One of our most frequently asked questions is answered below.  There tends to be a spike (pun intended) in cloudy aquarium questions after the holiday season has passed and all of the new gift aquariums get set up.  This might help if you’re a newbie!

Tom wrote:

I have a 90 gallon fresh water tank with a Fluval 405 canister filter. The tank is about 4-weeks old. I have been using Cycle to speed things along, but my water for the most part of 4-weeks has a white cloudiness to it. When I do water changes, the water clears up and then a day or 2 later it’s cloudy again. I have well water with a built in water softener and sediment filter.  My main question is, do you recommend the use of resins in conjunction with carbon to battle this problem?

From Marinebio@thatpetplace:

If the cloudiness is caused from particulates in the water, then yes a resin will help. If the cloud is from a bacterial bloom, which is highly likely, then resins will not solve your problem. Have you tested your water? Any ammonia or nitrite present? If either of those are showing levels above 0ppm, small weekly water changes of around 5% will help keep the toxic levels of ammonia and nitrite diluted, while still allowing you to cycle the tank. The trick is to keep the levels low enough to not lose fish, yet high enough to not to disrupt your nitrogen cycle and the beneficial bacteria that are trying to colonize. Large water changes can lengthen the amount of time it takes to finish your cycle, thus lengthening the time your tank stays cloudy. So if you can test the ammonia and nitrite levels, we can see where you are in your cycle.

For additional info on beginner aquarium basics and the nitrogen cycle view the following articles:




  1. avatar

    Some causes for cloudy water could be from overfeeding, too much direct sunlight (causing evcessive algae), or your tap water is cloudy. I use a chemical called “clear”. It only takes a few drops. It causes the small particles to co-agulate into bigger particles for your pump to be able to filter. Try to do a 20%
    water change monthly (change the filter cartridge when dirty). You hear different people tell you different amounts of water change at different time frames but be sure you do them on a consistent basis and use water conditioner. Your old freshwater also makes a very good fertilizer for your houseplants.Freshwater only!
    You also could be getting cloudy water if yu use live plants and they tend to decay. I have a friend that had bad tap water and they used bottled water. It worked great.

  2. avatar

    I have a 55gal tank. IN IT i have 3 huge oscars i cannot keep my tank or filters clean. do i need
    a diferent filter system or what?I don’t have a lot of money so what do you suggest?

  3. avatar

    Ihave a 55 gal aquarium with 3 large oscarsin it. I can’t keep it clean or fresh, do i need to change the filters or what? I’m just about ready to throw them away and they are about 7in. long. please advise me. my hair is getting shorter.

  4. avatar

    Hi Wilma. Sounds like the tank is overloaded. A 55 is barely large enough for 1 oscar as it grows and the filtration is probably having a difficult time keeping up with the bioload. They would probably require 20-25% water changes every 2 weeks as well as filter cartridge changes to keep the tank maintained well enough. You can try upgrading the filtration, but they will ultimately outgrow the tank, sooner than you may think. I would recommend that you take to oscars to a local pet store or give them away to someone with a larger tank to accommodate them. A 55 gallon is ideal for a freshwater community stocked with smaller fish with smaller max size like tetras, barbs, rasboras, ect. With smaller fish you should have an easier time with the maintenance and a better tank experience hopefully. Good luck.

  5. avatar

    I have just set up a 40 gallon freshwater tank because my smaller tank was getting crowded. The tank ran for two days and the water was clear. I moved my fish to the new aquarium and within a few hours the water turned cloudy. I removed two gallons and replaced it with fresh water and that helped just a little. What can I do to clear the water and make sure that I do not loose any of my fish.

  6. avatar

    You’ll have to leave the tank alone to let the nitrifying bacteria to restablish in the new tank. You can add Cycle or some other live bacteria culture to help the bacteria establish faster and monitor the chemistry, but don’t remove any more water or do any other maintenance, it will only perpetuate the cloudiness. Once the bacteria colonize (hopefully you have adequate biological filtration on the larger tank) the tank should clear, you’ll see the ammonia and nitrite levels drop and nitrate rise. Then you can do your first 20-25% water change. The water should clear hen the chemistry stablizes, just be patient with the new tank.

  7. avatar

    I just set up a 20 gal tank 4 days ago. Everything looked good until 1 day ago when the tank water got cloudy. How do I get the water clear again. I had the water tested today & they said everything was good & they told me to put some fish in the tank. The water is still cloudy & I am starting to lose fish. Please help.

  8. avatar

    Hi Michael…the water in your new tank should clear up on its own once the beneficial nitrifying bacteria colonizes in the tank. It is not uncommon to lose some starter fish, they may not tolerate the fluctuating chemistry in the tank as it cycles, and now that there are fish in the tank to contribute these bacteria, the chemistry will be more variable as the cycle starts and progresses. Don’t do anything to the tank…no water changes, no gravel cleaning, no filter maintenance, ect. just feed the fish once a day and continue to test the water every day or 2. The cloudiness is caused by the bacterial colony blooming and as the cycle completes the water will clear and ammonia and nitrite will break down to nitrate. When the water clears and the tests show no ammonia, no nitrite, just nitrate amounts (or no nitrates in some cases) you’re ready to do your first 20-25% water change and add a few more fish. The cycle can take a few days or a few weeks depending on how large the tank is and how many fish you have, you may choose to add synthetic bacteria (Cycle, biozyme, microbelift) to ease the cycle and speed it up.

  9. avatar

    Hi, I have a 10 gal tank and it took about 6 months to cycle and clear now I have changed the filter and its cloudy again I have about 10 baby guppys in the tank any ideas about what to do?

  10. avatar

    Hi Cathy. My guess is that the tiny guppies aren’t producing enough bacteria to maintain a bacterial colony. The tank took months to establish and clear because they are only contributing a tiny amount of wasste and bacteria to a relatively large volume of water. By removing the filter media, you probably removed much of the established bacteria so the tank is starting over. Is there gravel in the aquarium? What kind of filter is on the tank, and what did you change? Is the water tested periodically? Allow the tank to establish and clear again. You may not need to change the media for a very long time with such a small bio load depending on the type of filtration you have.

  11. avatar

    Got a 37galllon tank with 5 mollies and 2 plecos. the tank went through its bacteria bloom about a week ago. and is now doing it again. ammonia is high and im using a ammo lock to make it non toxic. nitrite has finally gone back to 0ppm. is the tank going through a anothe cycle cause i replaced my filter cartridge?

  12. avatar

    It’s possible that the balance of the aquarium was upset by the change in filter media, it’s also possible that the tank simply isn’t cycled entirely as you may see several spikes in nitrite and ammonia until the chemistry stabilizes. What kind of filter do you have? If it has more than on cartridge or media, try alternating your changes (one cartridge or media each time the maintenance is performed) to reduce the amount of beneficial bacteria removed. Once the tests read only nitrate present, you can do a small (20-25% water change, and this should be done every 2-4 weeks depending on how your chemistry tests.

  13. avatar
    Kristina williams

    I have a 37 gallon Tank with little fish. Cleaned gravel and changed some water after a month of the tank being set up and changed the filter. My tank is still cloudy. What can I do?

  14. avatar

    kristina, your tank is most likely still in the final stages of cycling, and the cloudiness that you are seeing is a bacterial bloom. Cycling typically takes 4-6 weeks to establish the beneficial bacteria in your filtration and gravel bed. You can add live bacteria cultures to the aquarium to speed up this process, from Microbe Lift is an excellent product for this. Cloudiness can also be from fine sediment or particulate matter in the aquarium, use of a clarifier like Seachem’s will clump together the particles and allow it to be trapped in your filter.

  15. avatar
    Kristina williams

    I went to the fish store and the ammonia level is high so I did a 25 percent water change and added nite out and a sea blend. Now my fish have the ich. I have been using ich attack for 5 days. Still see spots. Took water to pet store a couple days later and ammonia level was still a little high. I have snails Cory fish and mollies and tetras. What else can I do?

  16. avatar

    Kristina, Ich Attack is more of a disease preventative, than a treatment for Ich once it has established itself. Your water quality issues are probably at the root of you fishes health problems also, it is quite stressful on the fish, and will effect their immune system. I assume that you are using Ich Attack because you have snails and sensitive fish in your aquarium, which do not allow you to use more effective Ich medications that are formalin or copper based. I would recommend that you focus on your water quality issues first, the bacteria supplements that you have already used are a good idea, continue to use them following directions. You can also use ammonia removers like to detoxify, and help releive stress on your fish. Unfortunately, time is really the only real cure for your issues, your tank needs to finish cycling and stabilize.

  17. avatar
    Kristina Williams

    So how should I treat the ick if I can without harming the catfish and snails? Also how often should I do water changes to keep the ammonia down and to get rid of the ick? I took the charcoal out of the filter since I was using ick attack. I have been doing a 25 percent water change every few days. Am I doing everything correct or what else should I do. I use water conditioner before I add the new water. Should I be doing bigger water changes? Please let me know what I should be doing don’t want to lose my fish?

  18. avatar

    Kristina, 25% every few days is a very aggressive water change schedule, and could easily be adding to the stress in your aquarium, make sure that the pH and temperature are the same in the water to reduce the stress. Is the water conditioner that you are using just a chlorine remover, or is it something like Seachem or Kordon that is a more complete conditioner. These will remove ammonia and detoxify nitrite, but still allow your biological filter to function. Keep using the nite out according to instruction, and you can keep using the ick attack to try and prevent the disease from getting worse, you are very limited in medications you can use with invertebrates. If you have somewhere else you can put your snails, you can use a more effective ich medication that is copper or formalin based.

  19. avatar


    I have inherited a 120 gallon fresh water fish tank which traveled from AZ to CA. 45 fish took the five hour trip to CA. I used tap water with declorinator and conditioner. I did 10-20% water changes weekly and the tank was crystal clear for months. Two weeks ago I did a large water change 50% and cleaned my filters. I have had milky cloudy water for two weeks. I have tested my water (NO3, NO2, pH, KH and GH. All my levels are right in range. Again the water is still cloudy. I have been told to be patient but I think two weeks is a long time and its not getting better. Any thoughts? Would a bacteria supplement work? If so can I put it directly into the tank or should I do it during a water change? Thank you for any help you can give me! Garrett

  20. avatar

    Garrett, there are a couple of possible causes for your cloudy water. It could be a bacterial bloom caused by the shock to your system from a large water change and filter cleaning. Not sure what you mean by right in range with regards to your water test, and you don’t mention testing for Ammonia, if your water test for any amount of Ammonia or Nitrite, then a bacterial bloom is the likely cause of your cloudy water. Two weeks is a long time, but 45 fish in a 120 is quite a bioload, especially if they are being fed well. Adding a live nitrifying bacteria supplement will help to replace and boost your tanks filters biological filtration, and yes, this can be added directly to your aquarium. A good product to use is Ecological Laboratories Night out 2

    The other possibility for the cloudiness is from a fine particulate suspended in the water, this could have come from your water change, of from disturbing your gravel bed. You can use a water clarifier product to remove suspended particulates, clarifiers work by causing particulates to clump together, allowing your filter to trap them. Seachem’s Clarity, is a good example of a quality clarifier.

    Many aquarists will use both of these type products as part of their regular maintenance routine, to insure that they get the best results from their water changes, and a clear an healthy tank.


  21. avatar

    I have found by raising water temp. to 78-80 degrees I resolve the Ich problem.

  22. avatar

    I have a 55 gallon tank with i Oscar a jack Dempsey and a bottom feeder fish. I’ve had the tank for about 2 months and as I clean the tank and refill it the water still seems to be cloudy even though I have a 70 gallon filter. What do I do?

  23. avatar

    Hi James, What color is the cloudiness – white, brown, yellow, green? An Oscar and a Jack Dempsey is a lot for a 55-gallon tank and your tank is still very new and likely hasn’t been fully cycled yet. I would recommend reading through our blog “Why is My Aquarium Water Cloudy?” as well as the blog “The Nitrogen Cycle and Conditioning Period in New Aquariums“.

  24. avatar

    Hi i change my old filter to a new aqueon quiet flow 30, on a 30 gal freshwater tank.I have 3 fancy fish the water is do cloudy so worried dont want to lose any of my fish, i do about 25 percent water change maybe a little too often what could i do please help me. Also my shubunkin eye turned black, just one i was told not to worry can’t find any write up on this topic.

  25. avatar

    Hi Pamela, It sounds like you have the same problem as James, the last commenter. 3 goldfish can be very dirty, particularly in a smaller aquarium like yours, and an Aqueon QuietFlow 30 will likely not be enough to handle them. Goldfish produce a lot of waste and need to have ample filtration. Adding a new filter can also restart the cycling process. The color of the cloudiness – white, brown, yellow, green – is also a sign of what the problem may be. I would recommend reading through our blogs “Why is My Aquarium Water Cloudy?” and “The Nitrogen Cycle and Conditioning Period in New Aquariums” and also testing your water quality (Ammonia, Nitrite, Nitrate, pH at least) to help diagnose your problem.

  26. avatar

    I have a 37 gallon tank set up for a year with tetras and other small fish. I cant het my tank to clear up. The water is cloudy and even after water changes it still wont clear up. Any suggestions please would help. I use prime when i do water changes

  27. avatar

    Hello Kristina, I would recommend reading through through the blog “Why is My Aquarium Water Cloudy” as well. How often do you do water changes and how much do you change at a time? How soon after setting up the tank did you start doing water changes? Have you tested your water, and what are the values for at least Ammonia, Nitrite, Nitrate and pH? What color is the cloudiness – white, brown, green, yellow? All of these factor into why your water may be cloudy and how you can clear it up. You can also call and speak with someone in our Fishh Room at 717-299-5691 to help you figure out the best way to clear up your tank.

  28. avatar

    Howdy I have a 20gl tank with a 406 fluval the tank is filled with 15 gallons of water. It has a floating log. Natural and UV light and it’s all for one turtle. We change the water out all put in all null new charcoal and filters. After 3 days the water is extremely cloudy. Did allndllnd water test the tap water has a high gh level. All other levels are normal. We don’t have are bacteria bloom. We have done 3 tank cleans in 4 weeks but water is still cloudy. Do I need a water softener? I live in the city and get water from the tap. Please help I am at the end of my rope with this tank! 🙁

  29. avatar

    Hi Julie,

    Thanks for leaving a comment! It does sound like it could be a bacterial bloom. If you change out the water and change your filters at the same time, you lose all of the beneficial bacteria that has grown and developed since your last water/filter change. That bacteria will have to start growing again, and during that process it will make your water cloudy.

    Turtles create a lot of waste, so that bloom would start pretty quickly. A bacterial supplement would help it clear up quicker, but a better solution might be to try staggering your water changes and filter replacements so they are not at the same time. Change your filters once a month and do a water change the week before or after that change. Doing it that way would cut down on the amount of bacteria you lose at one time and you can cut back on the amount of cloudiness.

    Hope that helps please let us know if you have any other questions. Thanks!

  30. avatar

    Hello. I did a 15% water change in my 75 gal salt tank over the weekend. I have a diatom bloom going on and felt a water change and an addition of beneficial bacteria would help. Water cleared up fantastically for a couple days and now it’s starting to get cloudy again (Wed/Thur). Should I just let it run it’s course or should I do a water change again? Diatom bloom is still going on but not as fierce as it was. Also wondering if I’m leaving the light on too long? I have a yellow tang, maroon clown, nemo clown, bubble tooth anemone that the maroon clown hosts in and a dwarf fuzzy lionfish, along with some hermit crabs.

  31. avatar

    I meant bubble tip anemone!

  32. avatar

    Hello Chanda, I would recommend giving our Fish Room staff a call so we can discuss your tank in more detail. Diatom blooms are typically a sign of a new or unestablished tank. If the tank is new and hasn’t gotten established yet (under about 4-6 weeks or if you’ve don a significant water change other than the 15%), then it would be best to let the tank establish on its own. Otherwise, there may be something else going on that I cant diagnose from your comment alone. Tank lights should generally be on for about 8-10 hours a day (including any bright ambient lighting from a bright room or nearby window).

  33. avatar

    Thank you for your response Eileen. Well, I did the water change after I realized that the “bloom” could have been caused by my using tap (conditioned) water to replenish the evaporated water. Now it seems the cloudiness only appears while the brightest light is on. I have an anemone so I’m not sure if I should turn the light off for a couple days, or just use the blue light…any recommendations? All the fish are totally healthy and happy and eating well. Oh, I’ll also mention that I added some beneficial bacteria and it has helped clean up the rock and sand…could that be causing the cloudiness for a few hours per day along with the light?

  34. avatar

    Hi Chanda, I would need some more information to help you diagnose anything more specific. What color is the “cloudiness” – white, green, brown? What are your water parameter – salinity, pH, Ammonia, Nitrite, Nitrate, Phosphate? How long do you have the lights on now? You can reach our Fish Room staff at 717-299-5691, option 7 if you would like to discuss your tank in more detail.

  35. avatar

    I have a 150g tank with a new api filstar xp canister filter. The water is looking cloudy. Is that something that will eventually clear up or do I need to do some small water changes? Or maybe buy something to help? I fill it up with tap and use a water conditioner. Never had a problem with my 30. Maybe its because its so big it looks dirty?? Idk any help would be nice.

  36. avatar

    Hello Christina, What color is the cloudiness you are seeing? Cloudiness can be caused by a number of different things. If it is a white milky cloudiness, it is likely simply because the biological media in your new filter is still becoming established and it needs to go through the cycling process again but it is difficult to say for sure without knowing what type of fish are in the tank and more about the water parameters (pH, Ammonia, Nitrite, Nitrate, Phosphate, temperature, etc.). Another one of our blog entries, “Why Is My Aquarium Water Cloudy?”, may be helpful to you to help troubleshoot where your cloudiness might be coming from.

  37. avatar

    I have a 30 gal tank with an angel fish couple mollies, 2 tetras, 1 plecostomus. I have had it for a bout 7 months now and everything has been great! Yesterday I did a 60 percent water change and my water is EXTREMELY cloudy… I don’t know what I did wrong but I feel my fishes are not too happy with me right now. What could of caused this? I ha E taken this much water out before and have had no problems in the past. Maybe I need a new filter?
    Please help

  38. avatar

    Hello Jose, I will refer you to the previous comment to Christina’s question. A 60% water change is essentially starting your tank over and the cloudiness could be a result of the tank re-cycling but we would need more info about the water parameters to know more specifically.

  39. avatar

    Okay so after a few days the cloudiness was cleared so I’m going to assume that it was because of being a new filter. But now at the top of the tank there is a oily looking film. I can still semi see a current on top of the film. Is it my filter still? Aye, 15 years of fishtanks and I’ve never had a problem before.

  40. avatar

    Hello Christina, I would give your tank some more time to become established and be sure you are not overfeeding or using any types of lotions or soaps when doing tank maintenance. If you use frozen foods, try rinsing the thawed food in a small brine net before feeding with it to get rid of any excess fats and oils from the packing liquid. You may want to alter the flow in the tank to get some more surface agitation until the film clears up as well.

  41. avatar

    I ended up turning the out flow towards the top of the tank and added a bubbler. Film is gone and water looks good. I just didn’t have enough top water movement. Thanks for the response. 🙂

  42. avatar

    You’re welcome, Christina. Happy to help you get it figured out! 🙂

  43. avatar

    I have a 90 gal fresh water tank. The only trouble I have been having is the Ph keeps falling off the chart. Have to add Ph up weekly, and it is getting expensive. Any suggestions??

  44. avatar

    Hello Walt, What type of fish are in this aquarium and have you tested the other water parameters (particularly Ammonia and water hardness in this case)? Also, what type of water source are you using (tap water, well water, RO/DI water)? Ammonia is acidic and high levels will decrease the pH. Also, very soft water will allow the pH to fluctuate. If your Ammonia is zero and hardness is low, adding a buffer will help keep the pH consistent. Some water sources like filtered water from an RO/DI unit has all the minerals that help to buffer the water removed and will allow the pH to fluctuate; this source water should be remineralized or buffered before use. If your Ammonia level is high and causing the pH to crash, you will have to address that issue before you can fix the pH. Ammonia is very toxic and dangerous to fish.

  45. avatar

    I have 4 blood parrots, a crayfish and a placo. I use tap water with start right. To test I use the color changing test strips, and all other parameters are inline. I also do the 20% water changes weekly, and religiously. On the 4th week I do a 50% water change, and clean the canister filter as well as the hanging filter.

  46. avatar

    Hello Walt, Test strips are notoriously inaccurate and have a very short shelf life once opened. I would recommend having your parameters doublechecked. Without knowing the actual values of the parameters in your tank, the hardness of the water or how large these fish are, it sounds like you may be changing too much water and re-starting your aquarium every time. An established, healthy aquarium should never need a larger water change than about 25% and changing the majority of the volume will remove too much of the beneficial bacteria population that converts the waste into less harmful byproducts and keeps the tank healthy and stable. If you would like to discuss your tank issue in more detail, you can reach our Fish Room staff at 717-299-5691 or 888-THAT-PET.

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