I found this article and was very impressed with it. I thought everyone here at AquaTopiaForum.com would be able to benefit from it.

How Big a tank do I need?

--------------------------------------------------------------------------------

This site has one objective, to help you enjoy the hobby of fish keeping no matter what type of fish you are interested in. We want you to be successful, with many entertaining hours spent watching your fish.

When asking questions about fishkeeping here, you may have heard the word 'overstocked' thrown at your happy description of what you own. Here are three distinct ways you can be overstocked; each with pitfalls of something upsetting or boring happening in your tank if you do not follow each guideline for the fish you have or want.

1. Fish need room to move around

2. Aggressive fish need more personal space

3. The amount of fish must be sustainable in the volume of water


Explanations:

1. A good starting place would be that the tank should be 6x as long as the total length of the adult of the species you want to keep, and 2x as wide, and vertical height a minimum of half again the height of the fish. I may like vaulted ceilings but what makes a house livable is the square footage.

Daveedka’s experience:
------------------------------------------------------------
55g tank, two Oscars started out about 1", 2 25% water changes weekly. Filtration was an RFUG, and an emperor 400. No live plants.

“At about 6 inches the fish behavior simply became boring, no rapid movements, no hunting etc. At about 8" I would sell the fish and start over with 2 1" fish.”

“I have seen many full size Oscars in 55g tanks. Functionally it may be OK with exceptional filtration and maintenance, but what occurs is unnatural behavior, and this tends to make the fish less enjoyable.”

“We are in this hobby for entertainment purposes, and when we do things to lower the entertainment value we have essentially failed IMO.”
------------------------------------------------------------

For optimum schooling behavior more room is needed than the general rule for tank size. Greater than 10x the fish’s length and width of at least 5x the fish length is needed before a minimum of 6 fish will school some of the time. For larger schools the space should be increased to maintain the same behavior.

So give your fish the room needed to display the varied behaviors that are almost as numerous as there are fish out there. Research your fish to find out what the maximum size is. Your maximum enjoyment depends on it.


2. We get our fish and they will have room to swim when they grow up. But about the time they are half grown things start happening and in the end one fish kills everything else in the tank. Aggression becomes very limitating to what you can keep if you end up with a very aggressive fish.

Very aggressive fish like a breeding pair of 4-6” ‘neets or a potential 18-24" umbee probably won't share a tank even much larger than the above baseline tank proportions. Any attempt at adding fish to such housing would result in heavy bodily damage or death to the introduced fish.

But on the less absolute end of the aggression spectrum there are, for the most part, peaceful community fish that under some circumstances become terrors to their tank mates. For example, I had some serpae tetras in my 20 gallon that were absolute fin nipping terrors. A friend of mine was kind enough to take them off my hands and put them in his 29 gallon tank, and they are the peaceful community fish I had wished them to be.

A fish with a moderate aggression level can be caused to be more aggressive if housed in a smaller space than that fish requires for personal space. Each fish is different on that minimum. For example, 6 serpaes need closer to a 20x body length tank for low aggression levels to be expressed. I expect that many of the nippy fish like tiger barbs, serpaes, and black skirt tetras would be similarly peaceful if given more room. So the more aggressive a fish is, the fewer tank mates can be had up to the point where increasing the tank size does not change the option of zero tank mates.

One problem with asigning a value, or sayine one fish is more agressive than another, is the fact that the expression of the agression is up to the individual fish's personality and wheather or not that fish decides to beat the life out of the other fish or not. You can have a tank that is fine for a year and then one fish decides he doesn't want any friends and you have one fish left alive. The other factor is ability, Gambusia(mosquitofish) species can be very agressive, but don't have the equipment to do more than stress tank mates socially.


3. Good so far, I have chosen a tank I can afford (20 gallon tall) which has a 12x24 area so I am following the first rule and my largest adult fish will not be more than 4 inches. I am choosing fish that are peaceful so I don’t have to worry about aggression limiting my fish number.

So I get 6 bleeding hearts, 8 neons, 5 panda corries, trio platys, 1 Pretty pleco (Peckoltia pulcher), 2 blue ram cichlids, and a dwarf gourami.

Problem!! I do regular water changes of 25% a week and the level of waste in the water is not livable for the fish I have and I lose some. I could do more work but more work is less enjoyable if I have to do it no matter what.

I consider 1 cubic inch of fish per 10 nominal gallons as a reasonable baseline in considerations of what is fully stocked. However there are two things that affect the application of this idea: the numbers of a small fish needed to equal the volume of one larger fish will need more space, and the smaller the tank the less stable and more lightly stocked it needs to be.

One of the tanks featured in Takashi Amano's Nature Aquarium World is a 380 gallon tank with 9 discus, about 50 rummynose tetras, and the uncounted cleaning crew(ottos, amano shrimp). This tank's stocking level is about 3.34 cubic inches per 10 gallons with the 50 rummynose tetras being about the same as an aditional discus in volume. Larger fish like discus mean that the stocking levels tend to be higher even in large tanks like this, but the weekly 50% waterchanges, and abundance of growing plants, make this a very healthy tank.

To get your cubic inches of fish, measure the length width and height of the bodies of your fish. Multiply each individual fish measurement together and divide result by 3. That is the volume of one fish. Add each fish’s volume together to get the tank total.

Volume of a fish =1/3LWH


In closeing I want to say that there are to many variables to consider for any rule such as, 'x inchs of fish per gallon(s)' or 'so much surface area per inch of fish', to be even remotely valid in making any tank size suggestions based on a fixed rule. Even my observations about what seems to be a good ballpark figure is just the value at a cirtain tank size and other tank sizes will have slightly different values that are valid for that tank. So I submit that the assesment of how one can stock a tank is only as good as the completeness of the data used to reach the verdict.

Try to use the 1" per gallon rule and you will get how many inches of animated hairs you can have in your tank, doesn't tell me much about your fish which have width and height as well as length.


The equations for calculating above information

Li=adult total length of fish considered, or largest fish when adult
A=surface area of tank

A(Li)=12Li^2
----------------------------------------------------

Aggression is not concrete but I hope this gives some idea.

p=area space needed for peaceful cohabitation
T=area of tank, area given
a1=Agression tendancy level

a1=p/T

N=number of tankmates

N(a1)=1/a1

Generally when mostly peaceful species are considered

a1+a2+a3+.....a-nth<=1
-----------------------------------------------------

L=body length of fish in inches
W=thickness of fish in inches
H=depth of body or measure of fish from top to bottom in inches
f1=volume of fish
V=total volume of all fish in system
t=gallons of tank volume

f1=LWH/3

V=f1+f2+f3...+f-nth

V/t<=1/10

tank volume in gallons t=lwh/231

For the volume of a fish you do have to devide by 3 so as to not grossly overestimate it.

Just body length, width and hight without any modification would be a brick. Fish are rounded and the tails taper in width so not all of that brick of dimensions is ocupied by the fish. The best aproximation is that the fish fills 1/3 of the volume of the brick.

Some large mature cichlids may excede a third of the volume of that brick, but for most fish the given equation for determining the volume is sufficient for the purpose of general bioload level questions.

I don't see the point of getting more precise than this because feeding practices can create greater inacuracies than this particular measurement method currently contains.

Re-printed with permission from Frederick Miles aka SnakeIce at Aquariacentral.

reminds me of my maths class lol very interesting i always wondered about volume of a fish but never thought of making a estimation rule for it very nice indeed

And I used to always ask in Calculus... 'When am I EVER going to need that!' When stocking your tanks, of course! :lol:

Surely the guy in example 3 with the 20 gallon is kidding right?

Lost me in the math somewhere ... I'll just calculate useing common sense.

It really makes a lot of sense. Much more accurate IMO than the inch per gallon rule. Above all else, use common sense, you know? It might work filtration wise, but I've run into a few points here lately where the tank just LOOKS crowded. So I cut back a little and moved some of my tanks inhabitants around. Now the crowded 29 gallon is being turned into a saltwater tank and all the fish in there now have a MUCH roomier 40 gallon to play in.

yes, the 20 gallon tank in #3 is a hypothetical example of the third type of overstocking a tank.

I had a 20 gallon tank at the time and based my calculations on that tank. Larger tanks may have a heavyer load but smaller tanks need to have less bio load for the volume. Small tanks are less stable than large tanks.