Choosing Your Tank


Choosing Your Tank


            One of the most significant reasons why new aquarists fail is improper selection of the aquarium tank. For the purposes of this book, aquarium refers to the complete system—including the water, fish, decorations, equipment, etc.—while the tank is simply the physical container. No two aquariums are exactly alike, but tanks can be alike.

            The problem that many new aquarists encounter with regard to tank selection is simply a lack of forethought. That is, new aquarists do not understand the ramifications of various choices because they are not familiar enough with the equipment to be informed consumers. As such is the case, this section is devoted to giving aquarists basic information with regard to tank selection.



Types of Tanks


            When strolling through the pet shop aisles, the modern aquarist is exposed to a huge selection of tanks. This plethora of options can be troublesome if one does not know the ramifications of the basics of tank design. Here is how some of the users classify freshwater aquarium tanks:


math-only aquarium

“I see four general categories of tanks: a) standard glass tanks, b) vertical-stylized glass tanks, c) acrylic or plastic tanks, and d) "bowl" tanks.

Standard Glass Tanks are the fairly typical tanks that are rectangular in footprint and offer a near one-to-one ratio for width-to-height. These tanks are fairly easy to find equipment for, have a decent amount of surface area per volume, and tend to last a fairly long time. However, the glass can be scratched by algae razors or gravel, they are typically heavier than some other tanks, and are rather plain.

Vertical[-Stylized] Glass Tanks have a width to height ratio that exceeds 1:1.7, and have a small footprint relative to volume. Their unique shapes make them easier to fit into the home, they are more interesting to look at, and they will accept most standard equipment (with the exception of UGF plates or standard hoods). No less, their small surface area limits stocking capacity, there is usually a "dead zone" in the tank (a void that no species occupies on a consistent basis), and they tend to be a bit more expensive per gallon than Standard Glass Tanks.

Plastic Tanks are those tanks that are molded to shape and are often smaller than 15 gallons but larger than 3 gallons. They are often cheaper than some standard tanks when bought as a starter kit, can have interesting shapes, and fit in very small spaces that larger tanks could not. Yet there are problems with plastic tanks: they do not last a super long time, they often require highly specialized and expensive equipment, replacement parts can be difficult to find, and they are too small to offer much stocking variety compared to larger tanks.

“‘Bowls’ are any tank at or under 3 gallons in capacity. They are often very inexpensive and easy to manage [do not require much space consideration or special accommodations], but there are only a few species that can really do well in such small environments. As such, small tanks are best avoided by beginners if possible.”





“…I do [not] know about the classification of ‘bowls.’  I mean, as a class of tanks—small setups under 3 gallons—it [is] sound, but what about the connotation of "bowl?"  We [or at least I] have a very low opinion of keeping fish in your typical bowl: the rounded or nearly spherical little globe of water that houses a miserable fish with no heating or filtration. These are instruments of animal cruelty to a large degree and I [would] never recommend them.

“But there are some small setups out there that I do [not] think deserve the negative baggage that comes along with the world ‘bowl.’ Some highly efficient setups at the 2.5-gallon or so mark can make wonderful betta setups, for instance.  There are small filters available for these tanks and you can even find ‘junior’ heaters to provide warmth.  Now that I think about it, the majority house incandescent light hoods, which can be adapted to hold compact fluorescents… [This makes] live plants a more viable possibility. 

“I would [not] recommend [bowls or small tanks] for a beginner.  When I first got into the hobby, I kept bettas in bowls (still working on forgiving myself for it), and I was thrilled when I graduated to my first ‘real’ tank…

“…But for the most part, these tanks are hard to maintain.  With such a small amount of water, there [is] not much room for mistakes.  Fish do [not] forgive water chemistry fluctuations very easily, and it can be hard to keep constant values in those tanks.  They [are] awkward to clean unless you purchase one of those ‘mini-siphons,’ and they [cannot] house much more than a betta fish and  maybe a couple of invertebrates, like snails. 

“My point is, these setups work in some situations.  They are not suited for beginners, in my opinion, but they are viable and can be maintained.  I think that this sets small, complete aquarium systems apart from simple fishbowls, in which those necessities—filtration and heating, as well as light—are…not present. 

“…I was just thinking about all the weirdly shaped tanks out there that are larger than the typical plastic/acrylic sizes mentioned and made of glass.  Many of these are custom but some can be purchased at your local fish store.  I figure that some of them, like the bowfront tank, will fall under established categories (like the typical rectangle-shaped setup).  With some others, though, they [cannot] really be sandwiched into our general tank categories.”



 Male Betta





“Definitely no on bowls. Yes, they look pleasing with a tiny comet goldfish in it, but once the reality is divulged then the complications start to get out of control:

“1) No space. Bowls are rarely even over 2 gallons (it [is] just that no one buys them in a gigantic size). It [is] best to just buy a small (or nano) fish tank. Any fish housed in a bowl [of] about 1 gallon [in capacity] will be miserable. Bettas may look fine, but you have to get under the scales to see what [is] taking place underneath.

“2) No heating. Now this does [not] pertain to some temperate water fish, but tropical fishes—bettas  especially—have a hard time. Their metabolisms are used to…heated [water and a] fast-paced heart beat…Since bettas are one of the most popular fish to put in a bowl, you really begin to see how it shapes up.

“3) No filtration. Here [is] the whammy. Since filtration is such a big part [of] aquariums, the toxins and whatnot build up. With [regard to] the Nitrogen Cycle…the bacteria really have no place to call… "home". They [are] trying to get every little nitrite and ammonia compound but with no water circulation, how does it get to them? And then the problem with no surface agitation: Anaerobic pockets in the gravel [form] and the poor betta has to overwork its labyrinth organ to make up for the lost oxygen.

“4) Hard to maintain. In what aspect? Literally every aspect! Since the body of water is very tiny, the water can fluctuate in temperature and chemical [composition] faster than that of, say a 36 gallon tank…”





“Yes I totally agree on the ‘bowl’ post. To me, anything that [does not] have a filter, [heater], and/or lighting [could be considered] a bowl no matter what the size. And I have found that some of the smaller 2- or 3-galllon [tanks] are pretty good for quarantine especially if you [are] only dealing with one of your fish that does [not] look just right. I also have [a small tank] that I…put my guppy in when she is close to giving birth. [It is] a quiet, safe place for her.

“Also, a lot of people want to ‘try’ out the hobby before jumping right into a large tank, which…I think is smart. You would hate to start a…55-gallon then hate it. [What would you do?]”



“I like bowls and 2.5-gallon tanks for my bettas. I [do not] use filters, they [are not] necessary if you have live plants in there. And, as Nikita mentioned, they make mini-heaters and filters specifically for such tanks. I see nothing wrong with them, provided the person puts the effort into maintaining them that they would expect to put into a larger tank.

 “That said, I see them as inappropriate for a beginner's first tank for…the reasons mentioned above. I just wanted to say that if someone did have the basic knowledge and was willing to put in the effort, then there really is nothing wrong with [smaller tanks].

“I [do not] think any bowl smaller than [a gallon] should be considered, though. Those stupid quart- and even pint-sized bowls are ridiculous.”


Best Practices Summation:

·         New aquarists are advised to refrain from buying small tanks and particularly those without filtration/heating systems. The reason for this suggestion is that larger tanks tend to be more stable with regard to water parameters. On the other hand, too large a tank can be an irresponsible purchase as well in that a lack of interest in the hobby would orphan many more fish than abandoning a smaller initial tank would. Using the numbers given, new tanks probably should be between 15 and 55 gallons for best results.

·         Long, wide tanks are preferred to those that are tall and skinny. These tanks also have more stocking capacity and often fare better in mimicking natural conditions than some of the more stylized tanks.

·         Be aware of the availability of the equipment associated with your tank; refrain from buying a tank that may prove difficult with regard to replacement of filters, heaters, hoods (lamps, canopies, etc.), and other devices associated with keeping fish.

·         Be sure that the tank is maintainable and relatively easy to work with. For example, a 125-gallon tank can be a large chore to clean unless one owns a water-exchanging device. As another illustration, it is very difficult for the average person to reach all the way into a tank that is 30 inches tall. As such, it would be hard to clean or decorate.

·         Lastly, make sure you like it. Try to find a tank that appeals to you and maintains your interest.


Reference for Types of Tanks:


 (click for better resolution)


Fish Needs


            Now that the basic classifications of freshwater tanks have been established, attention is turned to matching fish to the selected tank. This is an important process because it is not the case that you can simply throw any assortment of fish into the tank and expect it to work. For example, no aquarist would expect a whale to be a good candidate for a 5-gallon tank or a shark to be suitable for the average home aquarium. Similarly, aquarists must take into account practical considerations when selecting a tank and the fish that will live in it.

            The basic considerations that need to be on the aquarist’s mind when looking at tanks are the potential sizes of fish that can be kept and the stocking capacity of a tank (how many fish it can hold). Thinking about these things helps keep expectations realistic. Also, realistic expectations prevents the disappointment experienced by many new aquarists when they figure out that certain combinations of fish and tanks just will not work.

            Here is what users had to say about the needs of fish:


math-only aquarium

“As budget is the primary concern for most new (and even experienced) aquarists, I tend to believe it is better to select fish based on the tank rather than select a tank based on what kind of fish you want. This tank-dependent approach allows us to formulate some general selection guidelines:

1.        Tank length determines activity level and size of the fish. Thus, a longer tank correlates to larger, more active fish.

o      Active Fish (Tetras, Danios, Rainbowfish, etc.) need a tank at least 8-10 times their own adult length in order to have enough space for active swimming. Therefore, the maximum size of an active species you should keep is your tank length divided by 10 (L/10=A).

o      Normal Fish (Most Cichlids, Many Cyprinids, Many Livebearers, etc.) need a tank 5-6 times their adult size. As such, the maximum adult size of a normal fish you should keep is equal to the tank length divided by 6 (L/6=A).

o      Sedentary Fish (Some Cichlids, Many Bottom-Dwellers, etc.) need a tank 4 times their own length to feel at home. This being the case, length divided by 4 is equal to the adult size of the largest sedentary fish you should keep in your tank(L/4=A).

o      Eel-Like and Nearly Stationary Fish (Spiny Eels, Bichirs, Plecostomus, etc.) need a tank at least 3 times their adult length. Therefore, length divided by 3 is the maximum size of [sedentary] and eel-like fish that you can keep in your tank (L/3=A).

2.        The footprint of the tank influences both oxygen exchange and territory creation. With regard to oxygen exchange, the more surface area that a column of water exposes at its surface, the more oxygen it will contain. Also, more surface area equates to less dissolved carbon dioxide if surface agitation is present. With regard to territory, a larger footprint offers more decoration space. This leads to more hiding places for the fish and better boundary lines for territorial species. This being the case, if two tanks have identical volumes, then the footprint should be considered as another indicator of future success.


A Well-Planted Aquarium with Neon Tetras


3.        Some fish are taller than they are long. For these fish, the tank height should be at least double their own adult height. Therefore, if the tank is 24 inches tall, then the tallest fish should not exceed 12 inches in height.”



“I would think that someone would be better [off] choosing the fish to match the tank, rather than vice-versa, unless the person is starting with a particular fish in mind.

“I would also add a blurb on the width (depth?) of the tank. For some reason, [I have] heard more than a few people talk about how proud they are that they got a long enough tank for the oscar they are keeping, but [do not] consider that the poor fish [could not] turn around very well [as the] the width of the tank was still shorter than the [adult] length of the fish.”



“…Most beginners and even seasoned aquarists have to select a tank first and fill in with fish based on [the tank’s] statistics. Most of us would love to have a tank big enough to house a whale, but there [is] a lot of baggage that comes along with our ‘dream tanks’—space, money, and resources (like equipment, food, and medicine). In most situations, we have only a certain amount of these things, and must select our aquaria around them. 

“I do think it [is] important to have a general idea the fish you [would] like to house before committing to a tank. After all, if you [are] going to purchase a 20-gallon tank and you really like zebra danios, it [is] clear that a 20-gallon long tank will be much more suitable than its cousin, the 20-gallon tall, even though the price, space, and resources required may be similar…”



“…A lot of times [tank selection] is based on how much space you have and the cost, of course, comes into the matter as well.

 “I myself have done both. I have gotten a certain size or [shape of] tank based on what sort of fish I would like to have and also have gotten several tanks then decided on what to house in [them] afterwards. There are way too many choices and thus [I have] 10 tanks.

“I would say that…most people buy according to their space limit and [available money supply]…

“…In going with this thought, the cost of fish is also an issue. Bigger fish tend to cost more and cost more to feed as well. [Also,] you [cannot] have as many different species in your tank either [if you select bigger or more expensive fish].”


            The net result of this discussion is that tank selection has a direct influence on the size, activity level, behavior type, and number of fish you can safely keep. This being the case, Best Practices dictate that a responsible aquarist answer the following questions and consider them when buying a tank:


·       What is the LENGTH of the tank?

·       What is the HEIGHT of the tank?

·       What is the WIDTH of the tank?

·       What is the VOLUME of the tank?


To aid new aquarists, here are some of the most common standard aquarium sizes and their respective stocking statistics (NOTE: All values are approximate and based on average levels of filtration, aeration, water chemistry, etc.):


Tank Size

Max. Size of Active Fish

Max. Size of Regular Fish

Suggested Number of Fish

10 Gallons

2 Inches

3.3 Inches

4-10 Fish*

20 Gallons (High)

2.4 Inches

4 Inches

5-14 Fish*

20 Gallons (Long)

3 Inches

5 Inches

3-9 Fish*

29 Gallons

3 Inches

5 Inches

4-13 Fish*

55 Gallons

4.8 Inches

8 Inches

3-9 Fish*

*The suggested number of fish is such that the higher number corresponds to the smaller maximum size of the fish while the lower number of fish corresponds to the larger maximum size.

            The above values are based on the length of the respective tanks. Also, the suggested number of fish is based on the maximal sizes of the fish that can be kept in the respective tanks. Therefore, if smaller fish are kept, then the relevant number of fish could be increased.


Reference for Fish Needs:



Physical Factors and Location


            Lastly, the aquarist must decide where in the home (or office, etc.) to put the tank. This action necessitates that the physical properties of the tank be taken into account. For example, a large, heavy 125-gallon aquarium would not be a good candidate for a second story or a good tank for a single person to try to move alone. With regard to these ideas, users had this to say:



“I suggest:

“Figure out where you want to put the tank before you buy it.

“Buy the biggest you can fit/afford otherwise you will wish you did.

“Make sure the tank is LEVEL or [you will] stress the joints.”



“I always take weight into consideration, well the empty weight since when its moved it will be empty. I have to make sure its small enough that I can carry/lift it alone (since I live alone) and that I can take it up a flight of stairs. For me, 60 [gallons] is about as large as I will go because of [the issue of weight] (according to Hagen, my 40 breeder…[weighs] nearly 60 pounds.

“If you [are] on a [second] floor apartment, make sure your floor can support the weight of an aquarium, [do not] assume your 125-gallon can be safely supported anywhere; always make sure the floor can handle the weight.

“The best spot for an aquarium, for me, is away from a large window, near electrical outlets, and away from a heating vent.”


African Cichlids



“1) The access to an electrical outlet

“2) …On which story of a building the tank is on. This is important, very important, in old structures. Even in new structures, try to keep the fish tank on the ground floor so there are no worries about the tank falling through the flooring. A 10-gallon tank upstairs is no worry, but a 55-gallon is a different story...

“3) Bolt it. I know this is really only applicable to areas with earthquakes, but it really is necessary. Bolt the stand to the wall behind it, otherwise the tank will fall over in what [would have] been a minor earthquake.

“4) Add a lip. This is only applicable to earthquake-prone areas…but I feel the need to say it. If the tank slides off the stand or out of place, only the lip will be able to hold it on the stand.” 



“The tank and all supplies should be positioned well out of range of any doors.  The resulting drafts and possible knocks from the door are dangerous to the security of the tank. [Editor’s Note:{Temperature changes and sudden sounds/vibrations can stress fish.}]

“Also, set the tank up out of direct sunlight.  Do not place the tank where it will receive light from any window, particularly during peak lighting hours of the day.  This will invite excessive algal growth and if the tank is too close to the sunlight [Edit:{receives direct sunlight in a closed room/environment}], you risk overheating. 

“…Any light that hits the tank from a distance can also pose problems.  Before you set up the tank, take a look around the area.  Is it across from any windows?  Does the sun strike near where [you are] planning to place the aquarium?  You may need to check this a few times in a day to determine if your tank will get sun at any point during daylight hours.

“If the tank has to be set up in an area receiving sunlight, invest in a good set of blinds.  When the sun is at its worst, keep the blinds tightly drawn to prevent excessive algae growth or overheating.

“…Another issue…is proximity to the faucet.   A tank that is inconveniently far from a water source is a real headache to maintain, [as] is having sinks that [will not] accept buckets or jugs for refilling. House the tank in a place [near] a bathroom or kitchen sink. If you have to put forth too much effort to maintain the tank, [it is] easy to fall into the trap of not doing proper maintenance.  Avoid this by [positioning] the tank well and investing in a water-change device if needed.”



“…Bolt [tank stands] even when you are not in an earthquake region for safety with small inquisitive children…Only use stands that are made for aquariums, unless [Edit: removal] you have the technology or knowledge to make sure that whatever you are putting the tank on will withstand the ENTIRE weight [of the complete aquarium system]. A lot of new aquarists do not take the weight of the water, ornaments, and substrate that is added to the tank into consideration.”



“Make sure your tank is located conveniently by electrical outlets and a sink.  It is useful to have a sink nearby for water changes.  Also ensure your tank is on a solid stand and that the floor can support it.”


            The advice given above covers all the concepts demanded by Best Practices in that these recommendations are definitely aimed at achieving the best possible outcomes. As such, I simply offer a short summation of what was just delineated:


When Selecting a Location for Your Tank:



·         Drafts/heat registers

·         High traffic areas (i.e., near doors or in hallways)

·         Places that receive direct sunlight

·         Floors that may not support the full weight of the aquarium system (a complete aquarium system, on average, weighs 11-15 pounds per gallon)


Seek Out

·         Electrical outlets

·         Sinks or places conducive to water changes


When Erecting the Tank:


·         Make sure it is level (using a foam pad between the stand and the tank can help in this regard)

·         Bolt the stand to the wall and add a lip if you live in an earthquake zone or have small children


Reference for Physical Factors and Location: