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1951 Rathburn Rd E

Mississauga, ON   L4W 2N9

How do I disinfect my aquarium? Safely using bleach.

#Sterilizing a fish tank is not a decision that should be made lightly. There are only a handful of reasons why someone should ever do this. If you have a problem with a persistent, deadly disease, you've received questionable equipment, or you're looking to shut down and store your aquarium and don't want it to smell in your home. In order to sterilize your tank or equipment, here's what you need to know.

A full reboot - nuking an aquarium

When I ran a fish room, I had the occasional customer who came in and told me about spring cleaning their fish tank. They removed the fish, emptied out 100% of the water, changed all of the filter media and soaked/boiled the gravel. They'd look at me like I was crazy when I explained why this was a terrible idea, and then sadly, they were in the following week asking why their fish had died. Fish tanks are not sterile or "clean" environments, bacteria, viruses, algae, amphipods are all normal things found in an aquarium. If you're looking to #springclean your fish tank (again, terrible idea) this is not the method. Have some algae on your glass? Buy a sponge. For perspective, the fish room I ran had 700+ aquariums, and we never had the need to do this. This is for when you need a hard reboot. Recovering from hemorrhagic septicemia? I'd sterilize my tank and equipment.

What to keep, what to throw away

You're about to destroy all life in your glass box - on purpose. That's ok and it's not as scary as you think. You need to determine what is the most effective method for what you are trying to accomplish, and how you prepare your tank for when you want to start it back up. Anything #porous should be disposed of. Floss, sponge, wood (unconfirmed), flexible airline tubing…throw it away. There is the potential to sterilize wood, but there’s no guarantee that the absorbent nature of the wood will allow for it to be completely sterilized. Seachem’s matrix and Eheim’s Substrat have tiny pores that allow beneficial bacteria to grow, and this can also be a place to harbor disease. Depending on how you sterilize your equipment, it may be a better option to throw out your porous filter material.

Pick your poison. Literally.

Your options are bleach, UV and hydrogen peroxide. Each has its strengths and weaknesses.

  • #Bleach – This kills just about everything. It’s the most drastic measure out of all of your options, and your best choice. In a 1:10 mixture (bleach:water), bleach is highly effective at disinfecting your equipment quickly.

  • Hydrogen Peroxide – Another solid option, and safer than bleach, 3% H202 is used as an antiseptic for wound treatment. The benefit of H202 is that after ~24 hours, H202 breaks down safely into water and oxygen. The drawbacks is that it is significantly more expensive than bleach, and its concentration needs to be maintained to be effective.

  • UV light – The good, old sun. Sitting your equipment and aquarium out if the sun is an option for killing viruses and bacteria. It’s also the cheapest option of the three methods, yet the least reliable. The sun is used to disinfect water in developing countries, but there isn’t a lot of data about using the sun to remove waterborne viruses and bacteria from infested equipment. It’s effectiveness also varies in controlled tests.

Let’s use bleach

There are all types of great bleaches on the market today for different purposes. Use original bleach.

There’s a general fear of #chlorine bleach in the aquarium hobby. We’re trained to avoid chlorine in tap water at all costs. Tap water containing more than 0.03ppm of chlorine can stress a fish, and this is a very minute amount. The good thing is that chlorine is very easy to remove. When using bleach, ensure that you’re using “original” bleach. Don’t use the splashless or other bleaches with additives.

First, #clean the aquarium with a sponge. Remove as much algae and detritus as you can. Follow all safety precautions on the product, using protective eyewear and gloves. Use a 1:10 bleach to water ratio and let the bleach mixture sit for about 90 minutes. Place any aquarium equipment into the fish tank, such as filters, heaters, decorations, etc. When bleaching filters, dismantle them completely so that the bleach makes contact with all parts of the equipment. Make sure you soak the rim of the aquarium as well.

After the tank and equipment have soaked, rinse everything thoroughly and clean off any organic material with a clean sponge. Clean the nooks and crannies of your filter pieces, wipe down the glass and rim of your aquarium. Rinse and strain your gravel. Once you’ve rinsed everything, do it all again. Bleach will leave a residue if not rinsed away properly.

At this point, you can let the tank and equipment dry overnight and do a smell test. If it doesn’t smell like bleach any longer, you should be good to reassemble your equipment and get your aquarium up and running.

The super safe way: Place all your equipment and gravel into the aquarium and fill it. Triple dose Seachem’s Prime and let the filled aquarium sit for 24 hours. Test the aquarium with chlorine test strips that you can pick up from Amazon or at your local pool store, just ensure that the strips can test chlorine at a low range from 0-2ppm.

Things you'll need

  1. Bleach. 1:10 ratio. Have a 30 gallon tank? You need 3 gallons of bleach.

  2. Several sponges for cleaning your equipment and aquarium.

  3. Safety goggles. Ensure you get goggles and not glasses to prevent splashes from getting in your eyes.

  4. Elbow length gloves. Your skin will thank you (and you won't feel like your hands are on fire!).

  5. Seachem Prime to dechlorinate your aquarium.

Starting over

Nuking an aquarium should only be done as a last resort, but it's not something that should be feared. Make sure you wipe off any old organic material, rinse well, and you'll be back up and running in no time.

Leave a comment, a question, or even a contradiction down below and we can learn together.

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Andrei Vexler is an aquarist with over 20 years in the fish hobby. Having run a fish room with over 700 freshwater and saltwater aquariums, Andrei found his passion in South American cichlids, particularly altum angelfish. Growing and wholesaling angels to the GTA and surrounding area, he shares his years of experience in his blog for advanced aquarists.