The "one inch per gallon" rule

guppy

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This is something that comes up fairly often and is rather misunderstood therefore I will attempt to clarify the original meaning of the general guideline of "one inch of fish per gallon of water".

This is a suggested guideline for a well maintained and filtered tank.
It does not apply to all fish as some have differing requirements.

Here is the part that is being misunderstood.

The "rule" does NOT refer to the length of the fish!

The "rule" applies to the cubic inches of fish in the tank.

This means that a 5" gourami should be measured in this manner,
length overall (5"),
thickness, (1/2"),
height, (2 1/2"),
so for this fish you multiply the following, 5x 1/2x 2 1/2, this gives you a total of 6 1/4 gallons of water.

For small fish like glo-light tetras you will end up with something like this,
1 1/2"x 1/4"x1/2", this comes to 3/16 of a gallon (about 1/5), and that gives you 5 fish of this size per gallon (quite reasonable)

For larger fish you end up with something like this, my example here will be a silver arowana at 24" long, 24"x 4"x 1", which gives you 100 gallons of water.

As you can see this works fairly well.

You do also have to apply some common sense and allow for such things as potential growth, the fish types' tolerance for crowding, and of course the width and length of the tank (a 24" gar will not work in an 18" wide tank even if the tank holds 100 gallons).

So please people, accept that this is just a generalized guideline to figure potential stocking levels, not a hard and fast rule.
Also remember that just because you don't like it doesn't mean you should slam somebody for using it.
And lastly, please don't flame someone by saying a 10" oscar doesn't fit in a 10" tank.
Of course it doesn't,
but the rule never said it would.
 

cichlaguapote

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Very enlightening. I never knew how that works. Through all the flaming always done I thought it was truly supposed to be 1" per gallon not 1 sq" per gallon. Great post.
 
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guppy

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Mystix212;1096745; said:
I get it much more thouroughly now. IMO I'd still feel safer to avoid the rule.

I don't blame you but it does provide a nice general ballpark for planning a new tank or for someone lacking in experience.
 

guppy

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Hey Ewurm, maybe that is why when you try to add a new fish it bounces,
two more general rules, 1) it should take more than a teaspoon to do a water change, and 2) the tank should contain more water than fish.
 
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ewurm

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guppy;1096914; said:
LOL
Hey Ewurm, maybe that is why when you try to add a new fish it bounces,
two more general rules, 1) it should take more than a teaspoon to do a water change, and 2) the tank should contain more water than fish.
That's why 20 water changes only takes 8 minutes.
 

snakehead121

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cool guppy, I have used a diffrent method befor. First you find the serface area (length by width). Then for your fish for tropical freshwater 12in. per 1in. of fish, for cold freshwater 28in.(I think it may be 20), and for saltwater 48in. And for fish that go to the serface to breath double the in. requierd.
 
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