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How to Safely Clean a Secondhand Fish Tank or Aquarium

I'm interested in pet fish, and I enjoy offering advice to aspiring fish owners.

This used tank is so dirty—how do you make it clean again?

This used tank is so dirty—how do you make it clean again?

How to Clean an Old Fish Tank

If you're anything like me, when you started out your new hobby life as an aquarist, you bought a secondhand fish tank. Secondhand fish tanks (assuming they don't leak), are an excellent choice for the newbie fish-keeper because they're less expensive than a new tank, which allows you to buy a larger one to begin with.

This is ideal because the most common cause of killing fish is having too small a tank and putting too many fish in it. Some professionals believe that one goldfish needs 20 gallons to itself, which means even putting one fish in the so-called 'beginner's' tanks they sell at pet stores is sentencing your fish to a short life of misery.

But How Do You Clean Them?

But let's say you've gotten your secondhand tank, it's nice and big, you're happy with the excellent deal you got for it, but now you want to wash it. You've looked around online, and all you can seem to find are hysterical warnings to NEVER put soap or detergent in the tank (nigh impossible to get out of the seals and can kill fish over a period of months) and to never put other cleaners in there either.

With all the warnings out there, one could quite easily be reduced to a quivering mass of confusion—but, never fear, you have come to the right place. You can safely and effectively clean a fish tank using the following natural (and, fortunately, quite cheap) substances.

Cleaning Supplies Needed to Wash a Secondhand Tank

  • Salt
  • Vinegar
  • A new bucket (one that has never been used with any household chemicals)
  • Approved scrubbing pads from a fish store (Be careful if your tank is acrylic, as these are very prone to getting scratched.)

You're going to need to have a set of cleaning equipment that is only ever used for the fish, as even a tiny drop of detergent in an old sponge can get into the water and start whacking your fish like a silent assassin. It is best to use scrubbing pads sold by pet stores because you know for sure that they have not been laced with cleaning products.

Why Use Vinegar and Salt?

Vinegar is excellent for removing hard water stains, and salt will clean out a tank nicely. Vinegar will also neutralize a lot of unpleasant fishy odors that secondhand tanks can develop if they have been sitting mostly empty with a bit of old water and gravel in the bottom of the tank.

How to Clean the Tank

The actual cleaning process is very simple:

  1. Use lots of salt (don't be shy!) and scrub it around in the tank vigorously with the vinegar.
  2. Rinse very thoroughly.
  3. There you have it—a clean tank.

Now, keep in mind, this is how you clean an empty secondhand tank that you haven't put any fish in yet. Don't go dumping salt and vinegar into a secondhand tank that actually still has the fish in it, or you will soon find them doing the tragic upside-down limbo of death.

Next Step: Check for Leaks

Once you have cleaned out the tank, fill it up and check for leaks. If there are any, you can use aquarium sealant to fix them up. Follow the directions on the sealant precisely, and don't rush things.

It is common for new fish-keepers to want to rush into getting fish in the tank, but this is how fish die. The process from getting a new tank to actually getting a healthy fish that isn't going to die can sometimes take up to a month, but it is worth the wait. There is nothing more disheartening than going to all the expense and trouble of setting up an aquarium only to find that all your fish are dead.

Next Step: Cycle the Tank

Once your tank is clean and you are sure it is sealed, it's now time to begin cycling the tank, a process which builds up a colony of good bacteria in the filter. These good bacteria will convert ammonia and nitrates, which will otherwise build up in your tank and kill your poor fish.


This is unnecessarily well written on August 03, 2020:

See name

Abby on July 01, 2020:

I accidentally used fairy liquid in my second hand tank but I am soaking my tank in vinegar /water/salt it is glass will my fish be ok?

G on May 31, 2020:

what is cycling your tank mean?

Erika on April 17, 2020:

what about Glo Fish ?

Pat on February 26, 2020:

What kind you salt do you use ? Table salt

SAL on October 29, 2019:

thank you. learned a lot and laughed along the way/ appreciate it

Shari on October 28, 2018:

Someone poisoned my 10" goldies with an unknown odourless agent in their outdoor pond, over 2 days I lost all but 3 tiny ones. It was a plastic pond so is there a chance that it can be cleaned to be deemed fish safe again?

DML on October 28, 2018:

I'm glad to know that I've been doing it RIGHT all these years.... Thanks for not having us go out & buying products to use when there is natural things for us to use.

Vicki Clark on June 30, 2018:

Most helpful - thank you!

THANGARAJ.M on June 16, 2018:

Thanks four u bro keep your idea methad following

Jani johnson on February 24, 2018:

I just bought a 2nd hand tank I think they may have wash it with house hold cleaner to clean it how do I now clean it out and make safe for my fish

Rose Wilmot on January 20, 2018:

Thank you for the advice on how to clean a used tank, I just bought a 50 gallon one and I'm new at all of this would you direct me to the info on cycling a tank please? Thank you for your time.

Rhead on January 18, 2018:

Make sure you rinse well, dry the tank and let it get plenty of light

amy on January 03, 2018:

Love your advice

Susan on October 26, 2017:

Husband put bleach and Dawn dish soap in the old gross tank we got to soak overnight. Can we still get it clean enough to put our one fish in it? Did we mess up to where we can't use this tank? Thanks

carrie on October 11, 2017:

very helful it help me to knowwhat to do thanks

Maria Ortiz on May 10, 2017:

Thanks for the info... I am a newbie and just bought a 2nd hand 55 gallon tank that is filthy. It's complete with rocks and figurines but I don't know where to begin the cleaning mission. If you have anymore tips please send my way.

Kyle Smith on March 26, 2017:

Thanks for the information very helpful.

But be sure when you use vinegar to use baking soda on all the surfaces afterwards to neutralize the acid from the Vinegar.

maureen on December 27, 2016:

thank you so much...Its going to be a big job but not as big as I thought.

Chandler on December 20, 2016:

I cleaned my fish accessories with Lysol bathroom blast. They soaked with water for 2 days they raised well and let soak for another 3 days in fresh tap water. Then I let them sit out and air dry. Can input them in the tank now?

Janie on December 12, 2016:

How long after cleaning to start flushing the tank

I am on my way to pet store to get a pump and a topper

Robin on November 02, 2016:

Do I use regular table salt ? & how much?

Bermand on February 18, 2015:

The wood is screwed togheetr (evenly spaced) with large 6” screws designed for joining landscaping timbers. The corners are then drilled using a long wood bit and 110v drill. Also drill three holes on long side and two holes on short evenly spaced. Hammer rebar into holes down into ground. You may want to trim rebar depending on length so it goes at least 2’ into ground below wood.

Hope Alexander (author) on July 15, 2010:

Good luck with your fish keeping, Steve :)

stevehtcyl on July 12, 2010:

This was exactly the info I was looking for thanks. I just got a 33gal tank today and it is an absolute state! I was wondering how to get it good again. cheers

doof on June 15, 2010:

dude that sucks

2k of fish

my parents limit me to barely anything close to that. $15 per petco trip

Barbara Bethard from Tucson, Az on May 14, 2010:

dont know how I missed your wonderful articles before!! I am still a newbie but mine are making babies so they are what do I do with them>well I give them to my neighbor as "new friends" for his ciclids lol

Silver Poet from the computer of a midwestern American writer on April 10, 2010:

Thanks for writing this hub. I appreciate your humor--"an acrylic tank scratches if you look at it funny."

stars439 from Louisiana, The Magnolia and Pelican State. on December 19, 2009:

great ideas

Hope Alexander (author) on September 29, 2009:

Oh dear, I can only imagine how horrible that must have been for you. The expense and the loss of the fish you loved. That is very good advice about the hospital tank.

sooner than later on September 29, 2009:

Good information. I got started with a 270 gallon acrylic bullnose. oooooooops. I cleaned it well and kept it well for 2 years, but I didn't have a "sick tank" for newly introduced fish and killed everyting I had in less than a week. $2K worth of marine fish down the drain. reall sad too. p.s. always have a sick tank.