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Old Tank, New Setup

Posted by Augusta Hosmer on

So, you've found a crusty, old fish tank and have no idea if it, or your plans for a new tank, will hold water. It's easy to see a grimy tank on the curb and think, "Well, that thing's never coming into my house." But it could be a diamond in the rough. Here are tips and tricks for finding and buying secondhand fishtanks, cleaning them up, and getting them in shape for new fish and aquarium plants. For a more detailed post on fixing up cracked/broken aquariums, check this blog post out! Biggest tip we can give you: be patient in every step of the process, and you could come out with a show quality tank at a steal.

How to Find Used Aquariums

I think everyone has a B-list superpower. My best friend's is finding parking, and mine is finding stuff on the curb for free. It's a fantastic idea to try to tap into this power if you're looking for a new tank. I got all but one of my tanks secondhand and can't recommend it enough even though I'm starting to feel like a wasteland scavenger. I found a 40 gallon just sitting in front of a drive thru dumpster, and a 55 gallon on the curb belonging to a guy who smirked at me and said I could have it for free if I could get it into my car by myself (Better believe I got that thing out of sheer spite at that point. Not sure who played whom in that situation, but it's a nice setup, now).

You can go about this a couple of ways. One way is to make a want ad online (or old school in the paper) for the tank you're looking for with the price you're willing to pay. "But no one will respond to an advertisement about a fish tank." You'd be surprised. In secondhand groups, I've seen a 125 gallon go for $30 because someone inherited a tank they didn't want and they found someone looking for one. 

This method could get you a tank almost immediatley, or you may have to wait a while depending on your area. There's no way to predict how successful it will be, but it's worth a try to get you a tank for a price point you know you're good with. 

The second method is to do the opposite and search for older tanks for sale on platforms like Facebook Marketplace, Craigslist, OfferUp, Ebay, and so on. I've also had some success finding fishtank stuff near me using NextDoor. 

In-person methods are also good options. Sometimes vendors at fish/reptile shows will have cheap, used, or overstocked tanks for sale. I found a cracked 10 gallon for $3 that way and repaired it for about $4 and time, and it's good as gold. I'm also always scanning thrift stores, flea markets, yard/garage sales, and estate sales for tanks, and have recruited my semi-unwilling friends to do the same for me. On that note, another easy method that gets overlooked is just asking friends and family members if they have tanks they don't want. Surprisingly, there are a lot of people who get out of aquariums and just put their tanks in the garage and forget about them. Grandparents, apparently, are notorious for this. 

Another great way to get good deals and meet other folks in the hobby at the same time is to look into aquarium organizations or conventions near you. Even if you don't find a tank right away, the aquarium community rocks.

Tips for Buying Used Aquariums

Okay, you've found a good selection on an online platform, or a used tank at a garage sale. What's next? There are a few things to keep in mind when you're picking out a used tank. 

First, plan ahead. If you're looking to buy a huge tank and you drive a Smart car, do you have an easily-accessible way to get your tank home and situated safely? Do you have cash or access to an ATM since a lot of in-person, third-party sellers don't have a way to accept cards? If you're having it shipped to you, have you taken extra shipping costs into account and established a safety net in case it arrives damaged? (Glass + UPS hasn't been a winning combination, lately). Do you have a good place to put it? Do you have or need a stand for it? Does something need to go into the tank right away, or are you just looking for another project to work on eventually? Do you want just the tank, or are you hoping it includes other accessories (don't assume the tank will come with a stand, lid, filter, etc. even if those are in the ad pictures).

Once you've answered those questions, you should be set to move forward and look at your options. For online ads, I'm always looking for the phrase "holds water." You can buy a tank for fish even if it doesn't currently hold water, but you need to know what you're getting into ahead of time and realize even if you work on it, it might leak in the future. The seller should be up front with this. Bonus points if they have a recent picture or video of the tank with water in it, though that's not always a guarantee there are no leaks. 

If you see the words "Reptile," "Terrarium," "Has been resealed," or "Needs resealing," the tank might hold water anyway, but chances are it'll need some extra TLC to make it work for fish and/or a planted tank. Tanks are sealed together inside and out with aquarium-grade silicone between each pane of glass. If those seals are damaged, or they've only been created for terrariums that won't have to withstand water pressure, they can leak slowly and make your life a living hell. If the setup is a regular glass tank that just happened to be used for a reptile tank/terrarium, great. But if it's specifically designed to be a terrarium by its manufacturer (like ExoTerra, ZooMed or something similar), you will likely want to look elsewhere, because the glass is probably too thin/the seals are probably too weak to handle the water pressure of an aquarium. You can try it or try redoing it, but regular ol' glass aquariums are just easier and cheaper, in my opinion. If the tank is one of the smaller, plastic ones, like the kits you find at Walmart, it likely doesn't have silicone seals and you just need to make sure there are no cracks or deal-breaking scratches before you buy it (I swear, you look at those things and they scratch). 

An old, seal-less plastic 5-gallon aquarium with a black light lid

An old, seamless 5 gallon plastic tank

If you're seeing the tank in person and can have the seller fill it up in front of you, that's best case scenario. There's no guarantee there isn't a very small leak somewhere you won't notice until later, but if it looks like it's holding water, you're probably good to go. Check the seals carefully and feel if any are loose, pulling away from the glass, or cracked. Look for cracks and chips in the panes of the tank. Even a small chip in the right place can blow out with enough water pressure. 

Also be sure to check the frames/supports. A lot of people just look at the glass and call it a day, but the wood, plastic, or metal holding the tank together are just as critical. Are they still solidly attached to the tank? Is the wood rotting, or is the metal rusted? Is there any noticeable damage? This is especially important in larger tanks.

If it's coming with accessories, be sure to check those, too. Plug them in and test them before you take them unless the seller has just tossed them in free as a bonus. Also, just a piece of advice from someone who accidentally acquired a hermit crab because of this: make sure the tank is empty. A lot of online platforms won't allow the sale of live animals, so people can't post them on there. However, sellers sometimes get sneaky and go around this by calling an animal "an accessory" since they technically do come with the tank. Come right out and ask about it.

One last tip: don't judge a book by its cover, or...um...a used tank by its stains. Don't be afraid to take home a gross-looking tank if that's all that's wrong with it, because the cleaning is often easier than you think it'll be. And you can get some awesome deals if it looks worse than it actually is and the seller doesn't realize it. As long as it's watertight, you can turn it into something epic. 

Before and after photos of a used tank - the top has tons of buildup/wayer stains, and the bottom is a planted tank

Before and after photos of one of my first used tanks, proving you can get some good out of a bad situation. It was cracked and pretty rank when I picked it up, but I'm still happy with this tank several years later after a little work (also, please just ignore the fact the tank is not on a good stand for it in the photo - this was taken before I realized I was good with plants and bad at physics and I've since completely redone it).

You Got the Tank Home. Now What?

Before you clean or put any other kind of effort into the tank, put it in a sink, bath tub, or other area that can get drenched without problems. Make sure the tank is supported and isn't scraping against any hard surfaces, then fill it up and leave it for a while (I usually leave my used tanks overnight to two days). This is an easy way to check for a slow leak, cracks you couldn't see, and other problems. I like to put a small mark in dry erase marker on the outside to measure the water level, too - just keep in mind if you leave the aquarium too long you'll lose some water to evaporation and it doesn't mean the tank is leaking. 

If there is a leak, you will need to see if you can make some repairs (Here's that link to our post on fixing cracked aquariums again: How to Fix Up Broken Aquariums. 100% sure your tank is watertight? Then it's time to clean and get it ready for fish.

The most common cleaning issues people run into with older tanks are algae, water spots/excessive limescale, and mold/mildew. 

Algae looks brown, green, or black/blue and has a way of growing back even if you think it's long dead, so dealing with it and keeping your used tank balanced from the moment you set it up again is crucial. For more details on dealing with algae in both new and established aquariums, check out this blog post on it: An Easy Guide to Aquarium Algae.

If you find a used tank covered in white, almost salt-like stuff, it's most likely limescale (calcium carbonate or magnesium carbonate accumulation). That comes from a buildup of elements found in hard water - which is good for your plants, not harmful for your fish in most amounts unless you have a soft water species, and is easy to clean off. 

Limescale buildup on the top of an aquarium and a filter; white, crystalized buildup on the glass/filter.

Limescale buildup on an old tank of mine - I live in a place with very hard water, so I'm scraping this stuff off all the time. 

To start cleaning a really dirty tank, I usually just hose it out on its side first to knock out most of the debris. Do NOT fill the tank up and then dump it out while it's full - you're putting extra stress on the supports and glass that way. Once that's done, you can use sponges and scrapers to get the rest of the worst off. After that, for a deeper clean? Congrats. Your house is about to smell like a salad. White vinegar is a cheap and easy way to clean up an old tank. I especially like it for limescale/water stains. As long as you rinse thoroughly and use a mix of vinegar/water to clean, any residue when you do your final fill will not harm your fish. Vinegar is a weak acid, and trace amounts would likely only very slightly affect your tank pH if you left too much behind. Wouldn't recommend using apple cider vinegar or other types - the white is cheap and gets the job done.

You can also use diluted bleach. Just be sure to rinse it thoroughly. 1 part bleach with 9 parts water (10% solution) and rinsing a lot until I can't smell bleach has always gotten the job done. Do not use soap. 

Once you've gotten your tank all cleaned up, have fun setting up a new tank! 

Dustin, as usual, has some great videos on used tanks. Check 'em out and give his channel a follow! 

How to Find Cheap Fishtanks and Where I Bought My Tanks

How to Buy a Used Fishtank and How to Patch a Cracked Tank

Comment, let us know what you want us to cover next, and tank on!


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