# one CUBIC inch per gallon

I've just read an interesting post by a senior mod on another forum. He was explaining that not only is the 1" per G rule only a rule of thumb, but that it was eternally misinterpreted. It should really be called one cubic inch per gallon.

So what he explained, was that you multiply height x width x length. This means that thin, long fish win out under this rule, and that wider fish loose out and require more gallons per inch.

pistorta
I'm confused, are you saying that the rule you referred to is: one cu. in. of fish/gallon?

How would one apply this to the dimensions of their tank? I think many would agree that aquarium surface area is the most important determining factor when deciding how many fish to keep, so my question is this:

Can the equation above be taken one step further to factor in aquarium dimensions as a longer, wider tank can house a greater volume of fish than a taller tank.

Dino
But you still lose out unless you subtract substrate, decor, ect.

I stil think it is better to know your fish and stock sensibly.

Butterfly
That's why the distinction for mass is added in when the 1 inch per rule is used. It is really only a guide line.
Carol

I dont' think the two are mutually excusive. As I say in the first post. It's just a rule of thumb, so yes, you need to add other factors like species sensitivity, tank shape, etc.

But the rule of thumb in inches rather than cubic inches is an misinterpretation according to this person, and what he's saying makes a lot of sense.

But you still lose out unless you subtract substrate, decor, etc.

I stil think it is better to know your fish and stock sensibly.

I mean cubic, not square. My bad. Just changed the title.

Yes, having a tall hex makes a difference in comparison to having a long (equal volumes). But that's just another factor, like species sensitivity.

I dont' think it should be used as the sole input to deciding how many fish to stock in a tank, but I think it's useful as a basic rule of thumb.
I'm confused, are you saying that the rule you referred to is: one cu. in. of fish/gallon?

How would one apply this to the dimensions of their tank? I think many would agree that aquarium surface area is the most important determining factor when deciding how many fish to keep, so my question is this:

Can the equation above be taken one step further to factor in aquarium dimensions as a longer, wider tank can house a greater volume of fish than a taller tank.

Yes, it's just a rule or thumb, as I say in the original post. However it must still be correctly interpreted.
That's why the distinction for mass is added in when the 1 inch per rule is used. It is really only a guide line.
Carol

darkwolf29a
I agree with that, Armadillo. That's the reason why I always err on the side of caution, in these regards.

For example, yes, I can live with 3 roommates in a 2 bedroom apartment. However, while it will work, it won't be comfortable at all. It's less stressful if there is 2 people in a 2 bedroom.

It's all about how much stress a species can take. Is an inch per gallon good for a tetra...maybe, but they can live with less space and be happy, since they are schoolers anyway. But, I can guarantee that my Oscar would be EXTREMELY unhappy if I stuck him in a 10 gallon tank, in spite of the fact that he is only 8 inches long.

COBettaCouple
I've not heard that before, but for fish under 1" in 1 or more dimensions, that rule would
seem to create very small water requirements. Say a female Betta was 2" long, .5" tall and .25" wide. 2 * 1/2 * 1/4 = 1/4 gallon

manjil
I agree with darkwolf..

Purely in terms of nitrate production to allow you to get away with once weekly water change, which what this rule of thumb is about, wouldn't that make sense?

They do survive in really small containers and don't get nitrate poisoning, even without daily water changes.

It's no good because it's cruel as the fish can't even swim in that, but from a nitrate production point of view?

Look at those sad, sad betta fish that survive in the small vases for years.
I've not heard that before, but for fish under 1" in 1 or more dimensions, that rule would
seem to create very small water requirements. Say a female Betta was 2" long, .5" tall and .25" wide. 2 * 1/2 * 1/4 = 1/4 gallon

0morrokh
I don't think the cubic in/gal rule is very realistic...I mean think of a Neon, 1-1.5 inches long, .25 inches tall, and...not very wide. That would lead to a super overstocked tank, since each neon would only need a tiny fraction of a gallon. Or a female Platy...2.5 in long, .75 in tall, .25 in wide = ~.5 cubic in. 2 Platys per gallon? I don't think so! Talk about nitrates through the ceiling!

The cubic inch per gal probably works better for super big fish, but the inch per gal works well for smaller, slimmer fish.

jsalemi
The thing about all these guidelines is that they're really derived from educated guesses based on years and years of experience with aquariums by millions of people. They represent collective wisdom that says, "fish thrive under one set of conditions, and don't do so well under a different set of conditions." They're good guidelines for someone new to the hobby, because following them prevents a whole bunch of common newbie mistakes.

As the fishkeeper gains more experience, he/she can begin to bend the guidelines a bit, and let his/her own experience with his/her own tanks be the guide.

It's like learning to drive -- you don't get behind the wheel and drive out to the interstate and do 75 on your first lesson. You stay on the back roads or in the parking lot and learn the basics without the complications that can arise out on the freeway first.

0morrokh
It's like learning to drive -- you don't get behind the wheel and drive out to the interstate and do 75 on your first lesson. You stay on the back roads or in the parking lot and learn the basics without the complications that can arise out on the freeway first.

Well.....some people do.

I totally agree with what you're saying though...the rules aren't set in stone, more like general guidelines, but often if you're an experienced fishkeeper it's better to go more by your experience than rough guidelines. However they are helpful to people who are just starting out.

COBettaCouple
I guess we could call that the "barely surviving" guideline at best. It seems to have way more "exceptions" than the 1" per gallon for small fish and 3-4" per gallon for large fish.

Yeah, you're right. I am making an extreme point, so really, to be reasonable, the guideline means nothing at all anymore in such circumstances.

To take it to the next level - which would totally defeat the point of an easy to remember guideline - it could be the greater of the cubic rule or the straight rule.

0morrokh
I'd be interested to see if the cubic rule actually works for large fish. Anyone know the dimensions of, say, an Oscar or other big fish?

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