An old fish tank is one of the most versatile household items you can repurpose, and there’s no reason to let it collect dust in a garage. Whether you want to sell it, convert it into something new, or give it away, you have more options than you might expect. Here’s what to do with yours.
Sell It While It Still Has Value
Used aquariums in good condition typically sell for 50 to 75 percent of their original retail price. A tank you bought for $200 could reasonably fetch $100 to $150 on Facebook Marketplace, Craigslist, or local aquarium hobbyist groups. Larger tanks (55 gallons and up) hold their value especially well because shipping new ones is expensive, so local buyers are always looking for deals.
Before listing, clean it thoroughly. White distilled vinegar dissolves hard water stains and calcium deposits effectively. Soak stubborn spots with undiluted vinegar, keep the area wet, and give it time to work. Rinse everything completely afterward. A sparkling tank photographs better and commands a higher price. Include any equipment you still have: filters, heaters, lights, and stands all add value to the package.
Check the Silicone Before Reusing It
If you plan to use the tank for anything involving water, inspect the seals first. Aquarium silicone has a practical lifespan of about 10 to 15 years. After that, the seals become brittle and prone to leaking. Look for any areas where the silicone has pulled away from the glass, turned white, or developed visible cracks.
Resealing is a straightforward DIY project if you’re comfortable with it. Scrape out the old silicone with a razor blade, clean the joints with rubbing alcohol, and apply new sealant. The key detail: use 100% silicone that’s free of mildewcides and other additives. Construction-grade silicone often contains chemicals that can leach into water, making it unsafe for fish or plants with sensitive roots. Look for silicone specifically labeled as aquarium-safe.
Convert It Into a Terrarium
This is probably the most popular second life for an old fish tank, and for good reason. Glass enclosures trap humidity, creating a miniature ecosystem where tropical plants thrive with very little maintenance. Even a tank with compromised seals works perfectly since you won’t be filling it with water.
The basic setup uses four layers. Start with an inch or two of lightweight expanded clay aggregate (LECA) or lava rock at the bottom for drainage. Cover that with a piece of window screen mesh to keep your soil from sinking into the drainage layer. Add a thin layer of activated charcoal on top to filter the air inside and prevent mold. Then add your planting substrate, typically a mix of sphagnum moss and potting soil.
Tropical plants that love humidity are your best picks. Creeping figs, ferns, mosses, and small tropical species do well in the enclosed, humid environment a glass tank provides. Many of these plants would struggle as regular houseplants because indoor air is too dry for them, but inside a covered tank they flourish. A closed or partially covered terrarium can go weeks between waterings once the moisture cycle establishes itself.
Grow Herbs Indoors
An old aquarium makes a surprisingly effective indoor herb garden. The glass walls let light in from all sides while creating a slightly warmer, more humid microclimate than your countertop alone would offer.
Start with about an inch of gravel or pebbles on the bottom. This drainage layer is critical because, unlike a pot, there’s no hole for excess water to escape. Cover the gravel with a thin layer of activated charcoal to keep things fresh and prevent the environment from getting overly humid. Then add a lightweight potting mix. If it feels dense or heavy, mix in some perlite so roots can breathe.
Water carefully with a mister rather than pouring directly. Keep the foliage as dry as possible and focus the water on the soil surface. Basil, cilantro, parsley, and chives all work well. Place the tank near a sunny window, or add a small grow light if your space is dim. Leave the top open for airflow, since herbs generally prefer less humidity than tropical terrarium plants.
Donate It
If you’d rather not deal with selling or converting, plenty of places will take a clean, functional tank off your hands. Schools often welcome aquariums for science classrooms but rarely have the budget to buy them new. Local animal rescues, particularly those focused on reptiles or fish, frequently need tanks for housing animals. Nature centers and libraries sometimes maintain small aquarium displays as well.
Post in local community groups or neighborhood apps and you’ll likely find a taker within days. The fishkeeping hobby has an active secondhand culture, and beginners are always looking for affordable starter setups.
Other Creative Uses
Beyond terrariums and herb gardens, old tanks lend themselves to a surprising range of projects. A 10 or 20 gallon tank works as a greenhouse for starting seeds in early spring, protecting seedlings from cold drafts while trapping warmth and moisture. Some people use them as display cases for collections, filling the tank with sand and arranging shells, rocks, or other items. A clean tank with a light strip also makes an attractive holder for candles or string lights as a decorative centerpiece.
Reptile and amphibian keepers are another natural audience. A tank that’s no longer watertight can still house a leopard gecko, a ball python, or a hermit crab without any modification beyond a secure screen lid.
Disposal as a Last Resort
If the tank is cracked, badly scratched, or otherwise unusable, disposal takes a little thought. Aquarium glass is not the same as bottle glass. It has a different melting point, and most municipal recycling programs will not accept it in curbside bins for the same reason they reject window glass and drinking glasses. Putting aquarium glass in your recycling bin can contaminate the batch.
Your best option is to check with your local waste management agency for bulky item pickup or drop-off. If the tank came with older fluorescent lighting, handle those bulbs separately. Fluorescent tubes contain mercury, and several states, including California, Massachusetts, Maine, Vermont, and Washington, prohibit throwing them in the regular trash. The EPA recommends searching Earth911.com to find a recycling location near you for mercury-containing bulbs.
Metal frames and plastic hoods can usually go in standard recycling. The glass itself will likely need to go in your regular trash unless your area has a specialty glass recycling facility.