Read this before using the inch/gallon "rule"

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AC Members
Aug 7, 2002
Edmonton, AB
Lately, I've been seeing a few people using the inch/gallon rule when it comes to stocking fish. This "rule" is a myth. I don't know how it came about, but this "rule" is no where near acurate when it comes to stocking a real life aquarium.

Think of it this way... if the inch/gallon rule was true... then I would be able to stock 6 fully grown convict cichlids in a 30 gallon tank, and they should all be happy. Is this true? Not even close. In reality, putting only two fully grown convicts in a 30 gallon tank would be pushing the tank's limits.

Why do you ask? There are a few things to consider when stocking a tank:
1.) Fish behaviour. Not just their everyday behaviour either. You need to consider how the fish acts when it eats. How it acts if it breeds. How it reacts to its environment (ie. planted tank vs. non-plant tank). You also need to consider how the fish will react to other fish you might be into the tank (ie. putting fish that nip fins with fish that have long fins). Whether the fish is an active swimmer or not also comes into play.
2.) Fish diet. Fish don't all eat the same things. Some fish require higher amounts of protein in their diet, while others cannot have much protein at all. The list goes on, but you need to insure that either you can feed the individual species of fish correctly, or that the diet of all the fish in the tank are compatible.
3.) Fish size. Yes, fish size is important as the inch/gallon rule suggests. However, what the inch/gallon forgets to mention is that fish are 3 dimensional creatures. There are more to fish than just their length. One inch of neon tetras cannot be compared to once inch of a convict cichlid.
4.) You also need to put into consideration what kind of filtration you have running. Generally, tanks with a higher stock of fish will have more filtration, compared to one with less fish.
5.) Tank shape. You also need to consider the surface area of your tank. Generally, its better to have a longer and wider tank, compared to a deeper tank.

There are many variables when it comes to deciding what to stock your tank with. Clearly, the inch/gallon rule is flawed in more than one way. The only way to really know whether or not your planned stocking will work is to do some work yourself. Research like crazy, and afterwards, ask questions.

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Purple is the color of Royalty
Jan 30, 2004
Columbus, ohio
Thanks Richer, It's so hard sometimes to get people to understand what it really takes to keep comfortable fish. Especially when they have the inch per gallon rule beat in to their head by so many books and LFS's


AC Members
Feb 18, 2004
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Yeah I definitely agree with your disagreement of the 1 inch of fish per gallon rule. There is another factor that can complicate things. Fish metabolism. Some fish are like living playdoh poop factories. This fancy swordtail I picked up excretes more than my 3 guppies and 1 beta combined. If I used that rule of thumb for swordtails I'd be changing the water in my tank everyday or every other day.

Know where it came from? I've seen it in many older and some newer fish books. The info in most of the books are narrow and outdated anyway.


Registered User of Fish
Feb 6, 2003
Nova Scotia, Canada
Perhaps it should be called the neon tetra rule as that is one of the only fish that can possible use it.

Good post.


AC Members
Mar 30, 2004
British Columbia, Canada
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Awesome post. I really wish I had been told this before I started collecting fish, I'm sure my goldfish wish the same thing. :)


AC Members
Apr 16, 2004
It must have came about many many ears ago when all you could get hold of was neons LOL :)


i is a gud righter lyke leela.
Jun 3, 2004
I Always Heard That The 'Inch/gallon' Rule Was Only True till The fish got over 3'', Then It Got Different.

But Hey, I'm Just A Newbie ;)
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