How to Disinfect a Used or Contaminated Aquarium with Bleach

So you just went through the horrors of dealing with a massive disease outbreak in your fish tank and you want to know how to nuke those nasties out of orbit. Keep reading to find out how to use bleach (yes, bleach) to thoroughly disinfect your aquarium, aquarium equipment, and accessories.

Materials for Bleaching

Okay, first things first: gather your materials. I put on latex gloves and old clothes that can get ruined. Also, get some bleach, a measuring cup, siphon or container for emptying out the tank, washrag or sponge to clean surfaces, and spray bottle (optional).

Should I Bleach It or Toss It?

Bleach anything that may have been exposed to the fish water, even accidental drips from your hands. So besides the tank, you'll need to clean the filter, heater, aquarium décor, nets, siphon, algae scrubbers, buckets you used, etc. Be aware that some of this stuff may get discolored because you're working with, well, bleach.

Some people say gravel is ok to bleach, but I personally dump all substrate (especially since I like to use sand and aquascaping soil). I also don’t bleach live plants, biomedia, filter floss, driftwood… anything super porous or closed off that might be able to retain the bleach.

Disinfecting Instructions

1. First, wash off all the debris with warm water. Don’t use any soap or other detergents (especially ammonia-based cleaners) that may react with the bleach
2. The next step is to make your bleach solution. Just a safety reminder: bleach is dangerous if not properly handled. Read the bottle for the full warnings, but don’t ingest it, don’t let it come in contact with your mushy body parts, and use it in a well-ventilated area (like outside). The recommended concentration I make is a 1 part bleach for 10 parts water (preferably hot water). In most stores near my area, they only sell 8% concentrated bleach (not 5% regular bleach), so that comes out to about 1 cup of concentrated bleach per 1 gallon of water. See the CDC instructions for more details.
3. To clean the aquarium, you can fill up the entire tank with the bleach solution and wipe down the outside with a washrag or sponge. You can also use a spray bottle to spray and wipe down all the surfaces. Let it sit for 10 min, rinse with tap water at least twice, and then let it air dry completely so that the bleach breaks down into harmless compounds (mostly salt and water).
4. To disinfect equipment or décor with lots of crevices, completely submerge and soak them in a bucket of the bleach solution (or in the tank itself). Rotate and agitate the items in the solution to get rid of any air pockets or bubbles. Soak for 10 minutes, rinse with water a couple of times, and air dry.
5. For a canister filter where you can’t submerge it, throw away all filter media and run the bleach water through the empty canister filter for 10 minutes. Don’t forget to use the bleach solution to wipe the outside surfaces of the filter, tubing, etc. Then flush out the filter by running it a couple of times with clean tap water mixed with lots of extra dechlorinator. Empty out the water and let it dry completely for the next 2 weeks or more.

Lesson Learned

Do not let anything that is even slightly damp with bleach solution back into your aquarium. Remember the canister filter that I cleaned out? Yeah, after a few days of drying, I set up the entire aquarium again and put my axolotl in it. Unfortunately there was a tiny bit of bleach left in the closed-off motor compartment of the canister, and it was enough to kill her. 😭 So the second time around, I let the canister filter sit empty for multiple weeks to make sure it was completely dry. To make extra sure all the bleach is gone, you can buy a test kit that measures chlorine levels. And when adding animals, maybe put a cheap, delicate plant (like java moss or some plant trimmings) or a pest snail in first, kind of like a canary in the mine, before you add your expensive dragon puffer.

The BEEP Rating

So how beneficial, easy, efficient, and proven is this method? In other words, what’s the BEEP rating? Well, given that the CDC recommends it for disaster zones and tons of aquarists have successfully used it for their aquariums, it’s definitely beneficial, efficient, and proven. However, I’m going to give it 3 out of 5 stars for how easy it is. You're working with bleach, there’s some measuring involved, and you have to make sure that everything is completely dry before reusing it. But in my opinion, this method is absolutely BEEP-worthy and I regularly incorporate bleach cleaning for used and contaminated aquarium stuff.

Question of the Day

How do you clean a used or contaminated aquarium? Comment below with your suggestions to share them with the fish fam community. Don’t forget to take time to enjoy your aquariums and I’ll see you next time!

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