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Glass vs. Acrylic

The Differences Between and the Debate About Glass Aquariums and Acrylic Aquariums

(The First Tank Guide)

Most aquariums are made of either glass or acrylic. However, many people don't know what the difference is - except that the acrylic tank is usually much more expensive. Often this results in the impression that the acrylic tank is better, though frequently unaffordable. This is not necessarily true. Both glass and acrylic tanks have their benefits and their drawbacks.


Glass Acrylic
Scratching Glass is very difficult to scratch. Scratching glass usually requires a relatively hard material and a considerably amount of pressure. You can scratch glass if you take a piece of uncoated aquarium gravel or a rock and rub it against the glass, or if you take a piece of metal and deliberately scratch the glass. However this is unlikely. Acrylic is highly scratchable. Often, despite the best efforts of manufacturers and shippers, the packing materials used to pack acrylic tanks will scratch the tank!. The tank can be scratched by a person brushing it with their clothing, jewelry, purse, back pack, or bag when casually walking past it in the store, and the tank can very easily be scratched when people are moving, loading, or unloading it. The inhabitants of an acrylic aquarium can even scratch the tank themselves, if they have any sharp claws, teeth, or shells... Because acrylic is so easily scratched, it is very important that you only use acrylic safe algae scrubbers when cleaning your acrylic tank, and that you make sure you do not accidentally pick up any pieces of aquarium gravel in the scrub pad when you are using it.
Of course, acrylic is also easier to repair when it is scratched. Acrylic polishing kits are available in many places, and these can be used to remove scratches on the outside of the tank. These polishes should not be used on the inside of the aquarium, as they may leave a toxic residue that could make the tank uninhabitable.
Weight Glass is denser and therefore heavier than acrylic. A glass tank will often weigh 4-10 times as much as an acrylic tank of the same volume. Acrylic tanks are lighter than glass tanks. This means that if you have to move an acrylic tank for some reason, it will be much easier to do so once the water is all out of it than it will be for its glass counterpart. This also means that an acrylic tank will be less strain on the structure that is supporting it than a glass tank will. However, remember that the majority of the weight of a complete tank is the water and decorations, not the tank itself, so you will not save a lot of weight by using an acrylic tank rather than a glass one.
Breaking and Cracking A sharp impact will crack - or in extreme cases, shatter - a glass tank, or at least one of its sides. This will leave you with a mess, no home for your fish, and possibly some significant damage to the area the tank was occupying. However, this is not an every day occurrence. The force required to break a glass tank is still significant, and is almost always the result of otherwise inappropriate behavior. Though a VERY sharp impact will crack or shatter a piece of acrylic, the amount of force needed for this damage is far greater than it is with a glass tank. On the other hand, almost any impact to an acrylic tank will leave a scratch or mark, even those that would not have marked a glass tank.
Shape Glass is relatively rigid and brittle. Because of this, it is difficult to make fish tanks from glass that are not rectangular in shape. Also, when glass is curved, it has a tendency to bend light, making things on the other side of the curved glass appear larger or smaller than they really are. However, some glass tanks with curved sides are available now. Acrylic is easily molded and formed into almost any shape that can be described - and some that can't. Acrylic also has less of a tendency to distort things that are behind a curve. Because of these two factors, acrylic aquariums are available in a very large number of shapes - not just rectangular.
Support and Rigidity Glass can support considerably more than its own weight over distances. Because of this, glass aquariums can be kept on stands with an open or incomplete top with little or no risk. However, the aquarium stand still needs to be level and the stand still needs to be strong enough to support the weight of the tank.
Also, because of this rigidity, glass tanks require less structural support at the top to keep the tank from flexing or splitting its seams under the weight of the water. Though some bowing of a tank is normal, excessive bowing can lead to split seams or fractured glass.
Acrylic tanks require a stand that will support the entire bottom of the tank, or else the bottom of the tank may pull away from the seams under the weight of the water. This is not true in acrylic tanks that have a substantially thicker bottom than would appear necessary.
Also, acrylic tanks require much more support across the top of the tank to keep the acrylic from bowing apart and either splitting seams or spilling water.
Strength The materials required to build a glass tank will be thicker than those required to build an acrylic tank. Though tempered glass does not need to be as thick as non-tempered glass for the same size of tank, the tempered glass will still be thicker than the acrylic necessarily would be for the same tank size. Also tempered glass cannot be drilled to accommodate any filter system designed to use an overflow. Acrylic does not need to be as thick to support the same water volume as glass does, and any acrylic tank can be drilled to accommodate an overflow system.
Refraction of Light Glass has a different index of refraction than water. This means the as light passes through the air, then the glass, then the water to bounce off a fish and get reflected back through the water, then the glass, then the air, the light is bent four times. Each time the light is bent, the image is distorted. Colors are not quite true, position is not quite accurate, size can be distorted slightly. The thicker the glass is, the more pronounced these errors become. This means that in tanks with particularly thick walls, the fish can be significantly distorted. However, most home and office aquariums, even large ones, are not large enough for this to make a significant difference. Acrylic has nearly the same index of refraction as water. This means that when you see a fish in an acrylic tank, the light has only be bent once or twice. Because of this, the only distortion you are likely to see is that the fish is slightly misplaced, but the size and color are true.
Clarity Glass maintains its clarity over time. The glass in a new tank will match that in an old tank, and if you have to replace a pane of glass in a used aquarium, the correction you will notice is that there are fewer scratches in the new glass. Many types of acrylic will yellow with age, particularly if they are kept under a full spectrum light or are exposed to direct sunlight. This is a normal chemical reaction in the materials that the acrylic is made from. Though this is getting much better, this is still a possibility. Also, because the acrylic is so fragile, it is very likely that you will be viewing your fish through a haze of scratches that will only get worse over time.
Cost Glass is easier to ship and requires fewer specialized tools to work with, so glass tanks tend to be less expensive than acrylic tanks. Acrylic tanks tend to be more expensive than glass tanks. This is not necessarily because the acrylic is better than the glass, though in some ways it is (and in others it is not), but more often is due to the shipping costs. In many cases it will cost less to make the acrylic tank, but after the first three or four have been too severely scratched in shipping to be sellable the cost to the aquarium owner is much higher than the glass tank.

Which Is the Better Choice, Glass or Acrylic?

Personally, I prefer glass tanks over acrylic tanks. However, if you are setting up a very large tank - 500 gallons or more - you will probably want to consider acrylic. Also, if you are interested in a tank that is not rectangular in shape, you would probably be best advised to investigate acrylic tanks. However, there are some good glass tanks on the market now that have curved faces and are very appealing, and have all the advantages of glass tanks.

What About Plastic Fish Tanks?

Some plastic tanks are available. These tanks are usually very small and are sold to unsuspecting individuals who mistakenly believe that a small tank will be easier to care for than a large one. These plastic tanks are also often sold a decorative kits for children with special themes like fairy tales or cartoon characters. Often these decorative thanks are configured in such a way that, rather than being difficult to filter like a small tank would be, they are impossible to filter. Though these tanks may look interesting and may be appealing to young children, they should be avoided in favor of a larger, healthier, lower maintenance, easier to care for tank.




"Thank you so much, I really dig your page and find it very helpful and interesting."
October 15, 2005
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"My 3 year old daughter desperately wanted a fish so the family troops off to the pet store and buys - you guessed it - painted glass fish. I thought, "Wow, pretty fish." [It] never occurred to me the terrible things that are done to make them look like that. Now after [an] awful heart-wrenching morning explaining to my daughter her fish is in heaven with God, after only a week, I decided to look up these fish and see what I did wrong. Well I figured it out, my mistake was not researching what fish I was buying. A hard lesson learned at the expense of my daughter. I will never understand how people can justify hurting another creature solely for profit. Thanks for all the info on these lovely but mistreated little fish."
March 22, 2003
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