5 Steps to Sanitize the Fish Tank – How to clean a fish tank with bleach

Whether you are setting up a used tank, having a fish disease outbreak or cleaning your quarantine tank, it is always advisable to sanitize it. Sanitize here basically means cleaning the tank and everything in it (well except your aquatic pets of course!) thoroughly to get rid of any possible parasites. This should include things that you use with the tank, such as your siphon as well.

Sanitize the Fish Tank

I never thought this is necessary until I learned it the hard way.

Why do you need to sanitize the fish tank? – My Lesson Learned

You see, I had an outbreak of anchor worm in my goldfish tank not too long ago. I thought treating the whole tank with medication will do the job and yes, the Fritz Mardel Clout medication did work and my goldfish got better. However after a while, the anchor worms came back!


Anchor Worm on Goldfish Closeup
Anchor Worm

Well… because anchor worms like most parasites go through different life stages. At certain life stages, they are dormant and are just chilling in the substrates, plants, decorations and tank’s surfaces, or just swimming casually in the water. So when you thought the problem has gone away, it is actually waiting there quietly to manifest again. Furthermore, the medications that you use may not be effective for every of these stages.

That’s why the best way to get rid of any parasite once and for all in the tank is to sanitize it, and I used household bleach to do the job for me.

Why household bleach?

Household bleach contains the active ingredient of diluted (3-6%) sodium hypochlorite solution which makes it safe for usage. Besides whitening clothes and removing stains, household bleach is also used for disinfecting and sterilizing purpose. This is because sodium hypochlorite reacts chemically with micro-organisms and destroys them.

It is easily accessible, cheap and safe to use with proper handling (please refer to the precautionary statements of the product). For the purpose of sanitizing your fish tank, please go for the regular ones instead of those that are mixed with other additives for better smell.

How to sanitize the fish tank?

Alright, so now you are ready to sanitize your fish tank and everything in it (EXCEPT for your fish or any other aquatic pets). These are what you need to do:

Step 1: Remove your fish (and other aquatic pets) from the tank

If you have any fish or aquatic pets in the tank, please move them to a separate tank or container. They should be quarantined and treated with the right medications.

Why do my goldfish keep dying?

Step 2: Remove objects, filter & Drain the water from the tank

Drain the water from the tank and if you have any substrates, decorations and plants in there, take them out. You will also need to take apart and remove your filter. All these will need to be sanitized as well to remove any possible parasites.

Step 3: Prepare the bleach solution

In a bucket, prepare the bleach solution by mixing 1 part of the household bleach with 9 parts of water. You will need to prepare enough of this solution as you will be soaking some objects in it. Besides that, fill up a spray bottle with this solution as this will be helpful with objects that are too heavy to move around, such as your fish tank.

For goodness sake, please wear gloves when handling chemicals.

Photo by Your Best Digs, CC BY

Step 4: Sanitize the fish tank and Other objects

For the fish tank: Using the spray bottle that contains the 1:9, bleach:water solution, spray onto all the inside surfaces of the fish tank. If you have other heavy objects in there that you could not remove, spray the solution onto them as well. Leave it for 10-15 minutes.

For other objects: For most of the objects (except for plants and plastic objects), you can opt to sanitize them through boiling them for around 5 minutes in water. This applies to the filter media as well.
When you sanitize your filter media, this will mean all the beneficial bacteria will be killed off as well.
Plastic objects will go out of shape in boiling water.

However if you can’t boil them for whatever reason, you can soak them into the 1:9, bleach:water solution that you have prepared for 10-15 minutes. As for most plants, you can soak them into this solution for 1-2 minutes.
Note: Not all plants can stand bleach, so please check it out before putting them in.

As bleach has whitening capability, your colorful gravel or decorations may come out “less colorful”, if you know what I mean. I have white sand in my fish tank, so this is not at all my concern.

Step 5: Rinse, rinse and rinse

After leaving them in the bleach solution for 10-15 minutes, you need to rinse them with water many many times to get rid of the bleach.

Fish Tank Water Test

With the fish tank, what I did was as I was filling it up with water, I wiped all the inside surfaces with a clean wet sponge. Then I drained all the water from the tank and repeated the process for another 2-3 times.

As for those objects that I soaked in the bleach solution, I rinsed them 2-3 times too before leaving them to dry.

So there you go, 5 steps on how to sanitize the fish tank.

As all the beneficial bacteria are killed along with the parasites, you will need to cycle the tank all over again before it is safe to put your fish and other aquatic pets back in. Click here for more information about cycling your tank.

So do you sanitize the fish tank often? What do you use and how do you do it? Do share your experience by leaving it in the comments section below.

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2 Replies to “5 Steps to Sanitize the Fish Tank – How to clean a fish tank with bleach

  1. Thanks for all this helpful information. We are going through almost the same issue (new goldfish infected with anchor worms in tank with healthy goldfish). We didn’t quarantine him. Sigh.

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