The aquarium hobby can be very expensive. One of the best ways to save a decent amount of money is by purchasing a used aquarium rather than a brand new one. Used aquariums can often be purchased cheap from people who are moving, upgrading, or getting out of the hobby.

We’ll focus on glass aquariums. Glass aquariums are made out of the same glass that is used in everyday windows and glass doors. It can be hard to tell the difference between very nice acrylic and true glass by sight alone. Glass will feel much harder and be more solid than the resin used in acrylic aquariums. Glass aquariums will also have silicone sealant in the corners to attach the panels together, whereas acrylic aquariums are welded together without sealant.

With glass aquariums you will want to check for age, check the seals, check the bracing and check for scratches. If a stand is included, you will also want to make sure it is adequate.

NOTE: We do not sell used aquariums or any used products. However, we would love to sell you some new products to go with your used glass aquarium.

Checking Tank Age
Glass aquariums can last a long time. However, that doesn’t mean they can be used forever. The silicone sealant of most well-constructed glass aquariums only lasts about 20 years. If the tank you are looking at is already 15 years old, and you are looking for one to keep long term, then you will want to look for a newer tank. Aiming for a tank that is only a few years old will help you get more use out of it. It can save you the stress of it succumbing to age and creating an emergency situation where your fish have no tank.

The age of an aquarium can be found out by asking the owner, or by locating the manufacture date on the tank. The most common location for the manufacture date is on the bottom of the aquarium, inside the tank overflow box, or inside the tank’s rim underneath the top trim.

Checking Seals
Even if a tank is reasonably new, you always want to double check the silicone seals. Neglect, age, and certain medications can cause issues with aquarium seals. The aquarium’s silicone should be either clear or black. Discoloration, such as yellowing or graying seals, can be a sign that the silicone has absorbed medications. These medications will be released back into the water slowly over time, poisoning certain animals.

The silicone seals should be uniform and free from any bubbles or nicks. These indicate that the seal is not in full contact with both pieces of glass. This can be a manufacturing defect or a sign of damage and age. No matter the reason, even a tiny bubble can quickly expand, burst, and lead to the entire tank falling apart. It is easiest to check for irregularities when looking through the glass down at the silicone rather than from looking at the side. The clear glass will allow you to see easily if there is any damage in the silicone.

Checking Bracing
Many glass aquariums, especially larger ones, have plastic or glass bracing either around the perimeter of the aquarium or across the top. This bracing is needed to preserve the structural integrity of the aquarium. It is very common to find aquariums where the bracing has been removed or damaged. You should never buy an aquarium that does not have the original bracing. The life of the tank will be greatly shortened due to the excessive stress placed on the aquarium sealant.

It is important to note that many aquariums are designed without bracing and the manufacturers use thicker material to compensate for not having bracing. However, tanks designed to have bracing were never intended to hold together without the braces. Always ask the seller if the bracing was removed or look up the original manufacturing specifications.

Checking for Scratches
Glass tanks scratch less than acrylic tanks, but they still can scratch. Once a scratch is in glass, it is irreparable. Often when the tank is dirty, empty, and dimly lit, it can be hard to see scratches, but once the tank is filled with bright aquarium light the scratches will be more visible. These blemishes have the potential to ruin the vanity of a beautiful tank. Bring a flashlight when looking at used tanks. Hold the light on the side of the glass panels to help you identify any scratches and determine if they are reasonable for you. Some scratches are to be expected with used aquariums. It is up to personal opinion to decide if they are okay aesthetically for your display.

Checking the Stand
While the stand isn’t part of the aquarium, stands often come with aquariums, and getting a proper stand is critical to the longevity of an aquarium. Aquariums should always be evenly supported across the bottom glass or bottom trim. Stands that aren’t level or have uneven surfaces will create pressure points that put abnormal amounts of stress on parts of the aquarium. This can often lead to premature catastrophic failures, such as breaking glass or seals that will send water out of the tank and all over your floor. Avoid any stand that has significant water damage, bowing, or warping. Bring a level to check the stand and ensure that it is flat before making your purchase.