How to Clean a Used Fish Tank – Make an Old Aquarium Safe for New Fish

So, you decided to save a few bucks by purchasing a used tank instead of a new one? There’s nothing inherently wrong with that, especially if it means you can afford a larger aquarium than you would have been able to.

The only downside is you must make sure you clean it extremely thoroughly before use. But don’t fear, because we’re here to tell you just what to do in our article on how to clean a used fish tank.

How to clean a used fish tank written beside a used aquarium, half filled with water, isolated on white

You can turn a dirty, grungy old aquarium into something that looks sparkling clean and as good as new, with the right tools and method.

Follow our instructions below on how to clean a used fish tank and you’ll end up with an aquarium that’s perfectly safe for your fish to live in, and you’ll have saved a few bucks.

Why is it Important to Clean a Used Fish Tank?

You’ve picked up a used fish tank—why is it important to clean it thoroughly?

Here we address a number of reasons why you should get any used aquarium spick and span before you put any living in it.

  • Assuming you’re purchasing an aquarium that hasn’t been used recently, it’s likely to be dirty and dusty from storage.
  • Used tanks often feature stains from algae and watermarks that must be removed before use.
  • You (probably) don’t know why the previous owner stopped using that tank—their fish may have died from a disease or bacteria that the aquarium is still harboring.
  • A clean aquarium is a much healthier home for your fish. Leftover dirt and bacteria could cause illnesses or provide unsuitable water parameters.

How to Clean a Used Fish Tank

Now for the main event—here’s how you clean a used fish tank, step by step.

It might be a somewhat time-consuming process, but don’t cut corners, as it could risk the lives of your aquatic friends.

Check for Leaks

Before you get started, we’d recommend filling the tank and leaving it for a day or two to check for leaks. Some people prefer to fill it up to the top right away, whereas others fill it gradually over the course of a few days. The method you choose for leak testing is up to you.

If you find a leak, you may be able to repair it. However, some leaks are in awkward places or too big to be worth the time and money it would take to fix it.

While some people check for leaks after cleaning, we prefer to do it before. After all, there’s no point in spending your time thoroughly cleaning a tank only to realize it’s unusable due to leaks.

Get Rid of Dirt

Once you know you’ve got a water-tight tank, it’s time to get scrubbing. You can’t use just any old cleaning product, as fish are very sensitive to some of the chemicals in household cleaners. Instead, we use white vinegar or apple cider vinegar to get rid of all that tough dirt.

If you use commercial detergents, there’s a very real chance of there being some residue left over that can pollute your fishes water, even after thoroughly and repeatedly rinsing to the best of your ability. In our opinion, it’s just not worth the risk, and it’s really not necessary. So use a vinegar.

A bit of elbow grease won’t go amiss, either. Algae pads or other approved scourers or scrubbing pads from an aquarium supply store will help you get rid of stuck on dirt, without scratching or damaging the glass—though you should exercise caution when using scourers on acrylic.

If vinegar and scouring pads aren’t enough to get stubborn dirt off the walls, try a good scrub with salt, which is a natural abrasive—any salt will work for this purpose.

Rinse it Out

Even though salt and vinegar are natural products, any significant traces of them left in your tank could be harmful to its new inhabitants (excluding, obviously, marine and saltwater fish). That’s why you must rinse it out thoroughly before you move on to the next step.

For this first rinse, we’d recommend using very hot water near boiling point, to help get rid of bacteria that might be lurking. That said, avoid putting very hot water into a glass aquarium that’s cold (if you’re cleaning it outside or in a garage on a chilly day, for instance), as the thermal shock could crack the glass.

Ideally, rinse it a few times (but only use hot water the first time), to ensure you’ve got rid of all the vinegar and/or salt.

Sanitize it

At this point, we’d recommend sanitizing your used aquarium with an antibacterial sanitizer specifically designed for use in aquariums. You can pick up these kinds of products at any good pet store.

Since the instructions for sanitizers vary between different products, you’ll need to follow the usage instructions on the package.

Rinse Again

Depending on the sanitizer used, you’ll probably have to rinse your tank once more. But, again refer to the instructions on your specific brand of aquarium sanitizer.

Cycle it

Now that you’ve got rid of any harmful bacteria and your aquarium is as clean as it was when it was new, it’s now time to cycle your tank to build up beneficial bacteria before you add any fish.

The process of cycling removes ammonia and nitrates from the water, making it safe for your fish to live in.

Cleaning Used Aquarium Accessories

When you’re buying a used tank, you may also acquire second-hand aquarium decorations, plants, gravel and other accessories, such as filters. These will need to be thoroughly cleaned, too.

You can sterilize rocks and other ceramic decorations by putting them in the oven at 200 degrees Fahrenheit for 30 minutes or simmering them in a pot of boiling water for 30 minutes. However, you should first use water and a sponge or scrubbing brush to remove any dirt and debris.

Used filters should be taken apart and thoroughly cleaned with brushes and hot water to remove dirt and bacteria. You should also replace any filter media, such as sponges or cartridges.

While some people recommend soaking in a bucket with a weak bleach solution to clean used aquarium accessories, you must be very careful to wash it off thoroughly, as traces of bleach could kill your fish. As such, we prefer to use other cleaning methods.

Final Thoughts

So that’s how you clean a used aquarium, thoroughly, but most of all safely, so you can be sure it’s a suitable environment in which to place your fish.

Buying a second hand fish tank is a great way to save money, and with a little thought and elbow grease you can bring an old aquarium back to it’s almost brand new glory.

Do you have any extra tips we’ve not covered that you can share with the community? We’d love to hear from you, so please do drop any suggestions into the comments section below.

Happy fish keeping!

Wendy Kathryn

Hi, I'm Wendy, the owner and creator of this website, an experienced fish keeper and avid student of the art since 2010. My aim is to help beginners avoid the many possible mistakes when getting started in this wonderful hobby.

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