Is Bleach Safe to Use in an Aquarium?

The answer is yes. When used in the correct concentration, bleach can be used to clean an aquarium. We recommend mainly using bleach when completely cleaning out an aquarium. This may be when you have had a fish pass in this aquarium or it has been in storage for some time. Bleach should be used when boiling is not effective.

Bleach is one of the safest and most effective methods for sanitizing an aquarium before the initial set-up. Many people are afraid to use bleach because they are afraid of its potency but actually it is perfectly safe if used correctly. We use bleach for sanitization because it is one of the most successful chemicals we have for disinfecting. It is commonly used in U.S. hospitals and is recommended by the Center for Disease Control. Bleach or Sodium hypochlorite (NaClO), is also safe for the environment. It breaks down very quickly, leaving mostly salt and water behind. Because it is a strong disinfectant that breaks down into harmless byproducts rapidly, it can be used to sanitize baby and pet toys, aquariums and yes it is even used to sanitize our water supply.

Bleach has the ability to kill most bacteria and fungi but also the ability to affect fish if not washed away after use. Ensure you thoroughly rinse away bleach after use.

How to Disinfect your Aquarium with Bleach.

  1. When buying bleach for aquarium cleaning, only use regular bleach like Chlorox Regular Bleach or an equivalent. Do not use bleach mixed with detergent. Detergents leave dangerous residue that can be fatal to aquarium fish.
  2. Using a typical household bleach (which is already about 5% bleach) mix 9 parts water with 1 part regular bottled bleach.
    Note: bleach breaks down fairly quickly so only make small quantities at a time and never store bleach in a bottle previously used with other chemicals.
  3. Wipe any debris from the aquarium with warm water and a paper towel.
  4. Spray all surfaces of the aquarium with the 10% solution you have just created. Sanitizing outdoors is also a good option.
  5. Let the aquarium sit for 10-15 minutes.
    Note: Bleach is a corrosive chemical and can cause damage to your aquarium if left too long. Do not allow it to sit for longer than 15 minutes.
  6. Rinse your tank thoroughly twice.
  7. Allow the aquarium to air dry completely. This will help to insure that the bleach solution has broken down into harmless byproducts.
  8. Once you set up your aquarium, fill the tank with water and use an aquarium water dechlorinator.


Disinfecting Other Aquarium Related Items

Aquarium gravel, decorations, filters, and heaters can also be bleached using the same concentration of water to bleach. You can either spray them or soak them in a bowl depending on what you are cleaning. Just be sure to rinse well and allow everything to air dry completely before putting back in the aquarium.

You can clean any aquarium related items that are glass, non-porous, plastic, gravel or rock. Using bleach on bright coloured plastic plants may fade them.
Note: Metal rusts quickly when exposed to bleach. As mentioned earlier, never allow bleach to sit on the item for more than 10 – 15 minutes.

Important Safety Information

Bleach can be very dangerous if inhaled or ingested. It can cause moderate to severe damage if it comes in contact with the eyes or skin. It can also cause discoloration or corrosion of some materials. Please view the International Chemical Safety Card before using bleach.

  • Do not mix bleach with other chemicals
  • Only soak for up to fifteen minutes
  • Do not use bleach in a concentrate higher than 10 percent

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Reader Interactions


  1. Anonymous says:

    Quick question, not sure if anyone will see or respond. If you leave a tank empty (with substrate still intact) how long does it have to sit before the bacteria would die off? Reason being my 36g bowfront has sand as a substrate, and it will be a huge project to get that thing cleaned out.

  2. Christie says:

    Great question but I don’t know the answer. I have also heard of people laying it out to dry to kill bacteria though I doubt if there is any science (readily available) that offers assistance to us hobbyists. A detailed experiment would have to be done looking at various kinds of bacteria, environmental exposures (sun, humidity, temperature), dry time, etc. It is probably not a true method of sanitization.

  3. Anonymous says:

    ….best to just get rid of all the substrate, and boil all plastic and or silk plants, decor ect. Replace with all new sand and or gravel. Clean out the aquarium as stated above or Ive had great succcess by adding 1 cup bleach to a empty 20 gallon, filled to top with water and let it set for a full 24 hours, drain it all out, and rinse several times.

  4. Martin says:

    i have bleached my ornaments in hot water as done before. a bamboo stick/plant, silk/plastic plants and resin figures. i have rinsed them thoroughly and put them back in the tank. the fish have all died and the tank smells of bleach. i am gutted. please can you help as now i want to replenish the tank. i still have the water in the tank. how can i insure that the tank and the ornaments will be clean from bleach and non hazardous to any new fish. and will my tank be damaged due to the bleach as i dont think there is a lot of bleach in it at the moment.. also will i have new tank syndrome.

  5. Anonymous says:

    Martin, you need to thoroughly rinse the tank, i.e. fill with fresh water, move everything around for a while (run your hads through the gravel, shake out the ornments and run the filters)
    Then drain completely, refill the tank, and double dose with dechlorinator (Tetra Aquasafe or similar). Run the filter again and shake out the insides (to get the dechlorinator everywhere). Then re-change the water with normal dose of aquasafe. Now you have a dead tank and need to recycle (new tank synfrome). Get a bottle of Stress Zyme or other bacterial starter, and dose according to instructions. In a week you can probably add fish again. Go easy with a fish or two at first. Then add more. Good luck!

  6. Christine says:

    What if you lost track of time and the tank sat for longer than 15 min? Is there any risk for the fish after the tank has been thoroughly rinsed and then dried completely?

  7. dustin says:

    My fish have ick and velvet. They and the tank are in bad shape iv put them in a new tank but now I have to sanitze the please tell me the bleach will work and how to prevent my little friends from getting it agine.

  8. John Marus says:

    I know it’s been some time since someone posted, but I live in Costa Rica, no heaters needed. I have only a 10 gal tank (because I’ve had bigger and just want something that reaches homeostasis. Anyhow, I have 4 (now) big angles, and three neon tetras (out of eight).
    I introduced some very small “pond” plants that at first looked cool, but soon over took the tank. Then everything turned blackish, regarding all the algae and natural stuff, and I had infestation of snails. All the sides turned green/brown and I couldn’t even see into the tank. My two glass catfish of two years died, one at a time.
    Today I saw this website, took out a cooler and soaked everything in 10% bleach. Cleaned everything, but get this, I took Tilex (of all things) and sprayed the tank glass inside, left it. Wash, rinse, rinse. Acted like a gold miner when cleaning the gravel. I reset everything, cleaning the filter and new carbon, filled it with tap water 9 gallons.
    Lots of dechlorinator, added back 1 gal of original water. Bought five new tetras today, and more upscale fake plants for them to hide.
    Everyone is alive! thanks for the site

    • Duh says:

      Did they die? That’s because tilex contains harmful chemicals that kill the fish. If we could use regular cleaning products in the fish tanks we wouldn’t need this tutorial

  9. John Marus says:

    ok, maybe it’s best if I give you an update tomorrow or a week, one neon bye bye

  10. Mary says:

    Well, Bleached the tank 5 days ago. let it sit. Put de-clorinator in and ran for 6 hours. I am draining now and will rinse a few times. I will add water and declorinate again and run it. I will empty again and refill before testing and putting the fish and 2 frogs back in. African Dwarf frogs. We will see how it goes. I cannot carry this tank outside to dry but have been told I can rinse several times and declorinate and everyone should be fine. I will let you know.

  11. Dr D says:

    For those of you who asked, drying will kill some bacteria, but not all. Many can survive for years in dry soil, for example, so being dried on a glass surface or substrate or filter is no different. The best way to disinfect is to first use bleach as described above, then remove water and air dry, then spray or apply 70% ethyl alcohol and allow to evaporate. That will take care of almost all pathogens of concern.

  12. Jean kaufmann says:

    I am so nervous to do anything with my betta (whom I call “fish” ) she is perfect (first time fish owner lol) , anyway I have to clean her home .. Best way ?

  13. Jean Kaufmann says:

    First time fish owner, ,like my betta nervous to clean ..ideas?

  14. Surabhi Singh says:

    what if the regular bleach solution available in my country is only 4 % concentrate?
    what would be the proportion of bleach and water ? And how long should i keep plants dipped in it?
    thanks in advance:)

  15. Linda says:

    I have used bleach in my tanks many times over the years with no problems. I don’t use it every time I change the water, only when it becomes necessary to do a “deep clean” when I get algae or a fish gets sick. I remove everything, soak the gravel and all the inserts (don’t do the air stone, though). I don’t really measure anything. I just use warm water and regular bleach. When I am done cleaning everything I rinse, rinse, rinse until I don’t smell anymore bleach then I treat the water with double strength anti-chlorine liquid. (I also use Stress coat when I have to completely change the water.) I turn on the filter (without the carbon insert) and let everything sit for at least an hour. To date, I have never lost a fish using this method.

  16. Bee says:

    HELP!!! I have a 19gal tank, which I purchased brand new, to re-home a rescue feeder goldfish. There seems to be something inherently wrong with the ecosystem in there because for the entire 2 months, I have tried everything short of completely removing all contents and bleaching the entire tank. Nothing works!

    Fish is aggressively gulping (but not for air at the surface) and swimming erratically, then just sitting on the bottom, gulp-gulp-gulping. Initially had issue with black fins but that went away when I removed the fish from the tank and put him in a glass (temporary) bowl.
    I’ve done dozens of water swaps, removed all living plants & moss balls. I tried a cycle of Microbe-lift (per fish store suggestion). PH tests high (even straight from tap) but I use AmmoLock & conditioner. I feel like I’ve exhausted every option. About 2 weeks ago I added another small goldfish but it died a few days ago (black fins). 🙁 My poor little guy is currently staying back in the bowl until I can get this figured out.

    Can I add bleach to the current water and run thru the filter? I’m worried the pump won’t get sanitized, but I also don’t want to damage anything. Or should I break it all down, empty the water and clean each piece individually?

  17. Peter Draddy says:

    Hi, Great site for information, the issue i have is my Betta, that my grand children gave me at christmas developed Extreme fin rot + other issues?
    I had it in a 15 ltr. BiOrb tank filtered via a air pump, heated to 78 deg.
    I had just completed a total tank clean, new filter changed monthly & cycled. As these health issues had just started a week before.
    I used Api Bettafix as per instructions, then Aquarium solutions Betta Revive near the end unfortunately to no avail.
    So now lm going to bleach sanitize every thing that l use !
    My question is when l sanitize can use the sanitizer more than once ?
    Or would it be better to just make fresh batches for multiple pieces of equipment, decorations, substrate?

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