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Welcome to our page. I have been keeping marine and fresh water aquariums for over 20 years off and on. We try to provide lots of up to date articles on maintaining an aquarium. We also have many awesome links on the right side bar to all things both Fresh Water and Salt Water Aquarium related. Things like Medicines, diagnosis charts, Fish Identification Databases, DIY Projects, Just to name a few. Quick Links to our tank Journals there as well.

Around here we like Salt Water Aquariums just as much as Fresh water aquariums. We don't mind although they must be "OddBall", "Predatory", or "Monster" Fish and when they are all three we are most happy!! So stay a while, poke around a bit and look through our collection of Angler Fish, Bala Sharks, Snoflake Eel, Plecostomos, Spotted Gar, Volitans Lion Fish, Polypterus, Damsels, and many assorted others...

We will be posting comments and pics here all related to keeping our fish. We hope you enjoy your visit.

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Sunday, May 30, 2010

Stocking large fish and Non Custom tank sizes

Stocking Large fish and Non Custom tank sizes 

I see a lot of people with different fish in different size tanks. Its a common question for newcomers to ask how to decide what tank can hold what size fish.  I don't feel it is my place to tell people what fish they keep in what tank. In reality if you were to ask me what size cage I would prefer to spend my entire life in, I would obviously say none at  That's not entirely true either because for now at least we are all confined to the planet earth.  Even in their natural environment the domain of any species of  fish is finite.  Our modest accommodations for our pet fish are tolerable at best. Before we condemn others for what they choose to keep their fish in we must also realize even a 10,000 gallon aquarium is as a mere "shot glass" compared to the body of water most fish naturally come from.

That having been said, from a humanitarian perspective when asked how large a tank one should have for any fish my thought is as large as you can afford and accommodate.  That isn't always practical so there are some minimum sizes that a fish can tolerate without exhibiting negative behavior or health issues.  My purpose of this article is to provide the hobbyist with the framework to make the best decision that suits their situation.

I often see veteran hobbyists quoting the adult size of a fish for their recommendations on tank size.  I agree as a final quarters for a fish it is important , I also strongly believe one should consider the final adult size of a fish before they buy it or try to get a tank for it.  My feelings on this topic differ from the common views in only one way.  Although a fish may become a foot or even longer as an adult many of the fish that reach such sizes are slower growing as they get older. Most fish older then juveniles come from trade-in's or auctions, or private hobbyists.  A very small percentage of non juvenile Fresh Water fish come from wild caught.  This means that if a hobbyist wants an adult or medium sized fish they must raise it from juvenile or buy one from a trade-in or private hobbyist.  Those fish would not exist in the market if it were not for people who buy them and raise them till they reach the limits of their tank and then sell or trade them.  For these reasons when I see someone who wants to get a fish that gets larger than the tank they currently own I'm ok with this concept as long as they are aware of the final size of the fish and know they will have to eventually either sell the fish or get a larger tank.  So it is in this spirit that I offer information on:
"Stocking large fish and Non Custom tank sizes".
The general "Golden Rule" of tank selection is basically that "longer and wider is better than taller".   This has mostly to do with the fact that air enters the water through the surface area (the place where the air meets the water) of the tank.  It is a common myth that the bubbles rising in a tank from an air stone actually add air to the tank water.  The truth is they only add air because they stir the surface which effectively exposes more water molecules to the surface which is the only place they can dissolve oxygen.  In the short time it takes a air bubble to reach the top of the water there is really very little of it (so minute that it really doesn't effect anything) gets dissolved into the aquarium.  We can achieve the same or even better levels of "D.O." (dissolved oxygen) in our aquarium by simply agitating the surface of the tank with the return from our filtration.  Many advanced hobbyist (knowing this fact) don't even own air stones or air pumps.  So this is why it is better to have a tank that is as long and wide as possible.  Since this allows the water to continually acquire as much oxygen as possible naturally without agitation of the surface.  Additional considerations include: Swimming room for the fish you intend to keep, the different strata (areas) of the tank that fish inhabit.

When it comes to recommending tank sizes for large fish, we often find even the advanced hobbyists advising people to get a minimum of 200 gallon tanks etc.  This is really not completely accurate.  As you read on you will notice that there are very specific tank sizes that yield progressive improvements in width and length of aquariums and for the most part most increases in tank volume is just a matter of the manufacturer making the tank taller.  Taller tanks are of little value in giving a fish more room to swim.

Tank Size::
There are basically 5 important aspects of an aquarium.  They are listed in the order of importance:

The above link is a very good representation of the standard (Non Custom) tank sizes available in the industry.
Lets look at how aquarium specifications are commonly displayed.  Take for example a 55 gallon tank.
The Specifications are 48" x 12½" x 21" Tall 55 Gallon Glass Aquarium:  The first number is the length of the tank, The second number is the Width also called the depth, the last number is the height.  The word "Tall" in this example is used to make the customer aware that the last number is the height of the tank.   
*NOTE* Aquariums are commonly measured and referred to(Named) by their outside dimensions, we should not be confused by this "Name" to think it is the actual holding Capacity of the tank.  Due to glass thickness and the physics of measuring somthing from the outside versuses the inside the capacity of the tank is always less than what the tank is "Named", In our example above the tank is called a 55 gallon however if we measure the inside dimensions 47 in L x 12 in W x 20 in H we find our 55 gallon tank only holds 48.83117 US gallons of water - This calculation can also be useful when determining the proper dosages of medication or additives to use in an aquarium.
When looking for a home for a large fish the actual dimensions are more important than the total gallons a tank holds.  In fact the first two numbers are very important indeed.

Lets first think about what our goal is. It is to make our fish as comfortable as it is affordable for us to do so within reason. Ok so what is the minimum required to accomplish this goal?  As an  example lets look at housing an Oscar (Astronotus ocellatus)  or perhaps a pair.  they can get up to 15" or more although the most common size of an adult is about 12".  Lets say we have an adult that is 15 " long. that means if we really want to afford this fish the minimum mobility neccessary we should think of the fish as a ball that is 15" in diameter.   Imagine moving that ball around in a fish tank.  This imaginary ball represents our fishes ability to assume any position and not have to bend its body or have parts of its body patruding from the water.

If you notice the dimensions of tanks. When one speaks of large tanks you  will notice there are basically four lengths worth consideration:. 48', 60, 72', and 98". A 48" tank is basically the length of three adult Oscars. That is not really a lot of swimming room.  Basically the minimum acceptable length for a 15" fish  is 72" (even that's only 4 adult Oscars long).

Width AKA: Depth
Now the width a large tank which is typically called the depth varies from 12.5" to 48". An ideal Minimum width for a tank containing a 15" fish  would be 18", this allows the fish room to turn around without having to bend its body.

On our reference chart above The heights of large tanks varies from 17" to 31" .  We should concider the habits of the fish we plan to stock when we look at height.  Here we ask ourselves the following:
What strata of the tank will the different fish we plan on keeping inhabit?  What is the swimming habits of the fish I plan to keep?  In our example of an 15" Oscar we need to make sure out tank is at least 15" in height so that our fish can point straight up and straight down yet still remain in the water.Looking at the available dimensions we would consider 17" the minimum height.

The cheapest choice is Glass.  It is also the heaviest and most resistant to scratches.  The alternative is Plexiglas  which is far lighter more flexible but more susceptible to scratches and considerably more expensive.  an additional advantage is Plexiglas has a refraction index which is much closer to water. this means, there's less distortion when you look through Plexiglas as water than when you look through glass.  You will find it very common for people to say you can easily repair scratches in "Plexi" while this is entirely true it should also be noted that each time you repair a scratch in "Plexi" you will make the area around the scratch appear slightly more "Clear" thus over time you end up with a non uniform view of your fish.

How many fish can go into a tank?

A home aquarium is a balancing act of many factors. Just to name the main few.:
The number, size, and metabolism of the fish you keep,
Surface area of the tank,
Available space in the strata of the tank that the types of fish you keep, inhabit (Bottom, Middle, Top),
Enviornmental stress,
Temperment of fish.
Interrelationships between different species
All of the above plays a huge role in the health and longevity of your fish in a "Home Aquarium."
When you ask people or search online about the capacity of a given tank size. The formulas used to calculate the proper capacity are basically templates to build in a certain level of safety to allow for mishaps and mis- calculations and things that there simply isn't enough time to explain properly to someone who possibly isn't familiar with this balancing act called the home aquarium. As with any "Cookie cutter" formula you can bend the rules. However before you can do so with any hope of success, you need to completely understand the relationships between each of the factors I listed above. You just might find that by the time you do fully understand the above principals you will no longer even want to overstock... - Which is the meaning behind the opening statement, and the reason many people have several tanks. 

As mentioned above the stocking capacity is decided by several factors however two of these factors stand very high on the list.  They are:
D.O. - Disolved Oxygen (Aeration of the water)
Common sense

There are two basic rules for tank capacity. These rules like most rules are designed to be simple and avoid lengthy explanation (and possibly boring new fish keepers like I am of the underlining principles. Giving a new user a simple Semi-fool proof guide to which to go out and succeed.

1) Volume Calculation rule - This is most popular one used due in part to its simplicity in explanation. (1 inch of fish per gallon of water.)

2) Surface Area Calculation rule - You seldom hear of this because it is more complex. (The surface area is calculated by multiplying the width times the length of the tank, the tank can be stocked with one inch of fish for each twelve square inches of surface area.)

Both of these rules assume that the fish are slender common variety and must be adjusted for bulkier/more active fish.

Adjustments to Basic rules:
1) Heavier Fish require 1.5 to 2 gallons of water for every one inch of fish
2) Heavier fish require twenty inches of surface area for every one inch of fish.

Since oxygen for the fish in a fish tank is basically supported by the surface area of the tank. In a fresh water tank both of these rules will cover you provided you have ideal conditions plus or minus a few notches in any one parameter (room temp, water temp and barometric pressure.).

Both of these rules allow for electrical failure under semi-ideal environmental conditions as mentioned above. This is the foundation for avoiding overstocking in which case the surface area of the overstocked tank would not be able to support the oxygen needs of the fish.

Now as hobbyists we like to tip the odds into our favor and agitate the water and stock plants. These things further increase the aeration of the tank.


  1. Great Article about Fish Tank
    I like it most...

  2. Such a great and informative post. This is really helpful especially for those who are beginners in setting up an aquarium.


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