Questions To Ask When Buying A Used Fish Tank

When buying a new fish tank, I always think about if I should buy it used or brand new. It is a big risk and you have to be sure that you get it right every time. Some questions need to be answered before buying the fish tank.

You should ask the seller what has been in the tank, how old it is, and how long it has been without water. Also if there are any cracks and also ask the seller to fill it up with water to be sure there are no leaks.

There is a lot to think about when buying a used fish tank. A lot of it is very important to get right, otherwise, you will have an accident. In this article, I will go through what to ask and what to think about when buying a used fish tank.

Where to find used fish tanks

You are in the thoughts of buying a new fish tank. When searching for fish tanks you will find fish tanks selling that are used. They more often than not go for a lot cheaper than a brand new one.

There are some places where used fish tanks are selling. Be aware that the person selling it might not be serious and try to cheat you.

If you get cheated you will be in a lot of trouble, having water everywhere and in the worst case, you have to fix your whole house of water damage. That will be expensive!

Facebook marketplace

Facebook marketplace is a big buy and sells part of Facebook. Here everyone can put up (almost) anything for sale. You will find sellers in your vicinity which makes it easy to find a fish tank that you don’t have to transport very far.

There are a lot of people selling so be very careful of who you buy from. Some are not serious and might give you a defective fish tank.

Usually, the fish tanks on Facebook marketplace are cheap. But they could be cheap for a reason. It is really important to do your research on the tank before buying a cheap one.


Craigslist is one of the biggest marketplaces in the world. Certainly in the USA. Here people are selling their fish tanks at different prices. The prices vary but are generally cheap.

Craigslist has different areas where you sell depending on where you live where sellers are putting up their adverts. Craigslist will also show you local results.

Note that craigslist is not for everywhere in the world. It’s mainly for North America. Also, some sellers are in Germany.

You probably have a local site similar to craigslist and you will probably find a used fish tank there.

Pet stores

Some pet stores are buying used tanks, fix them if needed, and selling them to customers as a used fish tank.

If going with this route you could be fairly safe that the fish tank is in a good condition and will probably not break. The name of the company is at stake so the company will be sure that the fish tank is safe.

This is also the downside of this alternative.

There are not a lot of pet stores willing to risk their reputation with the risk of a used fish tank breaking.

Also, when the pet stores are buying a used tank, they will be sure to get it cheap from you for them to be able to sell it for a higher price and make a profit.

This will make the seller not wanting to sell their fish tank to the pet store and instead sell it to a person and get more money for their fish tank.

You could ask your local pet store if they buy and resell fish tanks but chances are that they will not since it’s hard to be sure the tank is in a good shape.

By looking locally you will find persons selling their used fish tanks. Either because they don’t want to keep fish anymore, or they want to get a bigger or smaller fish tank to have other fish. maybe because they don’t have space for it.

But… Before buying a fish tank from a person, be sure to check the fish tank in person and ask the right questions to be sure the fish tank is in a good shape and will not break.

Questions to ask the seller

At first, when you meet the seller you should be getting an impression of the seller whether the seller seems serious or not. Take a look around the house to see if there are more fish tanks, being a sign that they know how to take care of a fish tank and fish.

You could small talk with the seller about fish keeping to get some insight into how much they know about fish keeping. The more they know, the higher the chances are that they know what they are doing.

What is included in the price?

When asking about the fish tank, which you should when getting to see it, is what is included in the price.

Chances are that you already know what’s included in the advert but you could ask it again, to be sure and be certain you don’t miss anything and don’t get disappointed about what you get to carry with you home.

What could be included in the price is a lamp, pump, filter. Those are components that you need for a fish tank and are usually sold together with the fish tank itself.

You could also get the stand for the fish tank with the price of the fish tank.

Of course, the more that’s included, the higher the price.

If the lamp is included, be sure to ask how old the lamp is. If it’s older than one year, you should change it either way and it’s not interesting keeping the lamp.

If it’s new, it’s something you want to be included since lamps could be quite expensive when buying a brand new one.

If you are wondering what it costs to start a fish tank, you could read my article on how much a fish tank costs. In the article, I go through every expense of keeping fish.

What has been in it?

Another relevant question to ask the seller is what has been inside the tank?

There have been cases where the seller is selling a terrarium as a fish tank and that’s no good. It could be due to the lack of knowledge from the seller. Or the seller could have bad intentions knowing it was a terrarium.

Terrarium is not meant to have a lot of water which makes them break when you fill them up with water.

Also, take a look at where the inhabitants of the fish are now. If you don’t see them, ask where they are now. If they keep them in other fish tanks they know how to care for a fish tank. If the fish are gone, the risk is that they died and the seller could have a lack of knowledge about how to take care of fish (and therefore the tank itself).

The fish could be sold or given away. That is fine. That is usually the case if the seller is discontinuing their hobby of keeping fish.

Ask to get the tank filled

When buying a used fish tank, be sure to ask the seller to fill the fish tank with water. A serious seller is willing to do it.

By filling the fish tank with water you will be able to see if there are any leaks.

The leaks probably are in the corners or edges of the glass. That’s probably where the silicone is bad. If there are any leaks, be sure you either can fix it yourself or skip on that tank.

Any sign of moisture outside the fish tank when filled could be a potential problem. There should be no moisture at all when the fish tank is filled. All of a sudden the tank could crack and you will get a lot of water all over the floor doing a lot of damage.

How long has the tank been without water?

You should also ask how long the fish tank has been without water if there is no water inside it.

The longer the fish tank has been without water, the higher the risk the seals are dry and need to be changed. Dried seals are a cause of leaks and a quite normal reason for leaks when buying a used fish tank.

At the same time ask if the seals have been changed before and if so, be sure there has been a proper job doing so. If the job of sealing it is so-so. Skip the tank if you don’t want to do it yourself.

What to check yourself

There are some things you have to look at yourself when seeing the fish tank. These are things a serious seller is telling in the advert as defects but you could never trust that the seller is telling everything.

First of all, take a look at the frame. If the fish tank has one. the frame should not be crooked or bent in any way. If it is, there’s a risk of the glass underneath it is cracked and could be a cause of a leak.

It is also a sign that the fish tank has not been handled with care before, which could be a problem with the tank holding up when it is at your home.

Not all fish tanks have a frame to look at, some are frameless which is fine, less to look at.

The next thing to look at is the glass of the fish tank if it’s cracked or chipped. This is probably quite an obvious step to do but a lot of people don’t look close enough. If there is a small crack or scratch on the window, it’s easy to miss it and that is quite often something that will be a bigger crack, releasing all the water from the fish tank onto the floor.

To check for scratches, cracks, and chipping, shine a light against the glass. You will get a shadow if there are any cracks. Small scratches are not something to directly skip the tank though.

Some scratches are fine, cracks are never fine though. You should get a feeling yourself if you are willing to risk getting that specific fish tank with the number of scratches you see.

Take your time with this step. It’s a really important step since in the end, it’s your evaluation that makes it or breaks if you buy it. When you have bought it, it’s all you if anything happens.

When looking at the tank, take a look at the seals in the corners and edges.

The silicone should be flexible and not dry. If the silicone is old or damaged it will be flaky and will not protect against leaking water.

You could buy a fish tank with a bad seal if you are willing to re-do it yourself. Most don’t since it’s not worth the hassle compared to buying a new tank with fresh seals.

The seal should be covering the edges well and there should be no air pockets under the seal.

What to expect when starting a used tank

When you decide to buy the fish tank, you need to have a plan to transport it safely. The worst that could happen is to break the fish tank the first thing you do, by transporting it.

When buying a new tank you will get packaging protecting the tank while transporting it.

When buying it used, it’s uncommon for you to get packaging to protect the tank. Either you bring it yourself, you order transport or you fix it without the packaging and take the risk of it breaking.

Once you bought it home, the fun begins. You should start by cleaning it. Clean it with vinegar and water. Remove most of the dirt with a sponge.

The dirt you are not able to remove you should be able to remove with a razor blade. It won’t damage the glass.

If you have bought a fish tank that needs to be re-sealed you should do it now.

Remove the silicone with a razor blade and add new silicone to the corners of the fish tank. Be sure every corner is covered properly and not leaving any bubbles or cracks in the silicone for water to go in behind.

It is better to use a little bit more silicone than too little to be sure that you will get a proper seal.

The last thing to do is to start up the fish tank. Let it cycle, just as you would with a brand new fish tank before putting in any fish.


There are some pros of buying a used fish tank. The main pros are:

  • It’s cheaper
  • You could get other things necessary included
  • The fish tanks could be in different size and shape, otherwise hard to get
  • When selling a fish tank, you will get some money back and not losing it all when done with it

Buying a fish tank used is generally a lot cheaper than buying it completely new. Don’t fall into the trap to buy the cheapest available. It probably is the cheapest for a reason.

Either it doesn’t sell because no one wants it, or it’s not well maintained, or the seller has bad intentions wanting to sell something just to fool you and get the money while you get a wet floor.

A cheap tank is not automatically a bad buy. It could be cheap because the seller might want to sell it quickly and therefore putting the price lower.

Even tanks that are bought at a pet store and directly sold second-hand should have a discount. There is a risk of it being damaged during transport and only the risk should motivate a discount.

If you buy it used, chances are you will get some things for “free” included in your fish tank. It usually is necessities as a filter, pump, and lights.

Most of the time the price tag will be a little bit higher if these are included in the listing but generally, you will get them cheaper per piece if bought as a bundle. If you developed a good contact with the seller you could ask or get offered free stuff to go with the tank.

There is a chance that you will get the fish in the fish tank for free even. Be sure you can transport it home if accepting fish. You should then have transport bags for fish and make sure the fish are not more stressed than necessary when transported.

When buying used fish tanks you might find one that has an unusual shape or are is a different size than normal.

That is when someone has made a custom-made fish tank which is an option when buying fish tanks. Be sure the fish tank fits your house so you don’t have a shape or size that does not suit or fits your house.

Also, be sure that the fish tank is properly made. Since it is custom-made, you could ask where it was made and search that company (if it is a company that made it) to see if there are any problems with their fish tanks.

If it’s homemade, be extra careful while inspecting the tank to be sure there is no risk of it leaking.

It’s always fun and could be challenging to have an unusual shape of a fish tank. Everyone will ask you where you got it.


There are some cons with buying a fish tank used. They are a few but it would be devastating if they go wrong.

That’s what makes it a risky business to buy used fish tanks and not recommended for beginners. If you miss one small step, you will have a leaking fish tank!

The cons are mainly:

  • You have to clean the fish tank thoroughly to not get diseases
  • There is a risk of it leaking

Now, you have to clean a brand new tank too but it’s more important to be thorough with the cleaning of the fish tank when it is used. There will be algae and minerals stuck to the glass of the fish tank which makes it ugly-looking.

There is also a risk of it containing bacteria and parasites which makes the cleaning process more important. If you put fish inside an infected fish tank, the fish will get sick and they might all die.

You also have to clean the tank thoroughly because otherwise, you might get unwanted inhabitants in form of snails that have been living in the tank. The eggs could be stuck to the glass of the fish tank and hatch when you put the new water into it.

The riskiest part of buying a used fish tank is that it will start to leak. This is the part that scares most buyers of fish tanks. If you buy a new from the factory you will have some sort of guarantee of it holding.

If you buy it from a private person you don’t have that guarantee which makes everything on you if it’s breaking.

Most people don’t have bad intentions and would not sell a fish tank that is obviously broken and will leak water. But it’s easy to miss something and that could get a lot of consequences.

Therefore it’s very important to check the tank before buying it and be 100% sure the tank will hold.

What is impossible to check is the history of the tank. A small bump five years ago might have caused a microscopic crack that’s not visible and could be bigger and destroy the fish tank 5 years later.

Those things are impossible to know, even for the seller and that’s why fish tanks that are used are generally cheaper and also should be cheaper. It’s for the risk you take when buying them.


Most fish keepers buy their fish tanks brand new. They want to pay the premium and have a good night’s sleep knowing the fish tank will hold.

But you could save a lot of money if buying used fish tanks.

The important part is to look after the right thing and not completely trust the seller. Of course, you should trust the seller of what they are saying, but think about what they are saying and if it sounds likely.

It could be due to a lack of knowledge things don’t add up. If it doesn’t feel right, don’t buy the fish tank.

If the fish tank looks good and you get a good feeling from the seller, go ahead and buy it. As long as you looked for scratches, cracks, chippings and that the seal is fine you should sleep well at night and enjoy your fish during the day.

I would never recommend buying used fish tanks for the beginner though. It’s too much that could go wrong and the consequences are too high of a price to pay if the smallest thing goes wrong!


I have been a fish keeper a big part of my life. During the years I have gathered and searched a lot of information about fish keeping and here, on the website, is where I share that information to help you with your fish keeping. I want to provide the information that I didn't get when I had a question about my fish tank.

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