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Old 08-17-2011, 10:31 PM   #1
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Getting the Dirt on the Inch Per Gallon Rule and Stocking

Many people starting the hobby are mis-informed about exactly how many and what type of fish they can keep in a tank. For example, I've seen someone at a local fish store recently asking about why their chinese algae eater was growing so big and attacking other fish in their five gallon tank. I have also seen instances on other forums where beginners asking questions are mis-informed and say it's alright to keep red-tailed black sharks in a ten gallon, because they have had success with it and all was well.

In addition to giving away fish not suitable for the size of a tank, local fish stores also use the "inch per gallon" rule. Basically, for every inch of fish, you must have one gallon of water for. So, for example, if you kept six neon tetras, their max size is one inch. That is six neon tetras. Thus, you will need six gallons of water because that is six inches of fish. So basically, a two-foot pleco would need twenty-four gallons of water, a bala shark would need twelve gallons of water, a dwarf gourami would need two to three gallons of water, and so on and so forth.

This rule has many faults. Here is a a quote from a book I got at the library a year ago (The Complete Fishkeeper, by Joseph S. Levine) and have been renewing and checking it out ever since. Although it's inaccurate on some topics and outdated, it's much more useful than other publications. Contrary to most, it explains the nitrogen cycle in-depth, why small tanks aren't good habitats for most fish, why saltwater is not something to start off with, and most importantly, why the inch per gallon rule does not work.

Here is the section that explains the inch-per-gallon rule:
" 'How many fishes can I keep in my aquarium?' is the most common beginners' question. many books recommend 'one inch of fish per gallon of water without aeration, two inches of fish per gallon of water with aeration.' That formula has caused more grief to more fishes than any other bit of misinformation. In truth, such formulae all fall short, because stocking density depends on sizes and personalities of fishes, filters used, tank shape, and water temperature.

"Furthermore, you should realize that there are two ways to approach this question. Usually, the beginners are really asking, 'How many fishes can I stuff in my tank without them all turning belly-up in the morning?' It makes more sense to ask, 'How many fishes can coexist comfortably in my tank, in a way that allows me to keep things running with minimal effort?'

"The answer is not necessarily straightforward. No matter how large your tank, it is infinitesimally small compared to natural habitats. On a reef or in a pond, individuals of aggressive species have plenty of room in which to avoid one another once a contest between them has been decided. But even a fifty-five gallon tank-which most of us think of as quite large-offers little refuge for the vanquished, who can be continually harassed by the victor. And even generally peaceable fishes may harass one another if crowded too small in a space.

"For these reasons, it is particularly important to observe warnings about species that do not get along with others of their own kind. Nearly everyone knows that male Siamese fighting fish won't tolerate one another, but there are many other, less flamboyant species that fight just as intensely. In nature, their aggressive behavior spaces them out with many yards between them; in tanks, without room to roam, they fight both more frequently and more intensely.

" There are also some fishes-such as the giant danios (Danio malabaricus)-that are peaceable but very active swimmers. Such species fare well in ten-gallon when small, but need much more room to swim when three or four inches long.

"That's why experienced aquarists stock tanks more by intuition than by calculation. Two dozen large cardinal tetras in a twenty-gallon tank, for example, present an entirely different-and far more peaceful-situation than two dozen half-grown cichlids of the same size."

What I thought was important I wrote in red. Although it is a bit inaccurate, for the most part it tells you why this rule does not work.

Let's go back to the common pleco. According to the inch per gallon rule, this fish needs twenty four gallons of water. However, that is not a suitable environment for this fish at all. Even if the tank was twenty four inches long, it is still not suitable for this fish because a) it has a huge bioload that can easily overload most filters in that small of a tank, and b) in that small of a tank it can easily stunt itself, which is a process where the fish do not grow to their potential size, and their organs are squished together. It is a highly painful process for fish.

Let's also go back to the neon tetras. Although small, these fish are very active. Putting them in six gallons of water will do you no good, because these fish need much more swim room than that. A ten gallon is far better for these fish than a six gallon.

Make of this what you will. You can either continue to use the inch per gallon rule, stop using it if you are, or if you have already stopped keep informing people of why it is important to be responsible and choose fish wisely. No common pleco-no matter how bad of algae eaters and how messy they are-deserves to be stunted in a ten gallon tank because the aquarist keeping them was misinformed on the "inch per gallon" rule.

Keeping fish alive requires putting them in water, but keeping them happy and healthy requires research, effort and responsibility. Choose wisely.
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Old 08-17-2011, 10:36 PM   #2
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i use the inch per gallon rule but also know about those circumstances where it dont always work lol. like a 10 inch pirannha in a 10 gallon tank bs thats not happening lol. good write up!
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Old 08-17-2011, 10:42 PM   #3
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AWESOME write up! I have seen so many newcomers swear by the inch per gallon rule. It is simply illogical. There is no way to have a rule that is set in stone pertaining to aquarium stocking, experince is a much better way to stock an aquarium.

There is no place for the inch per gallon rule in the aquarium hobby IMO.
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Old 08-17-2011, 10:54 PM   #4
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When I got my first aquarium, I started stocking by this rule, but then I revised my stock later. It is of course highly flawed, but it did give me a decent guideline to BEGIN with. Of course, the inch per gallon guideline only helps when people realize it is not concrete, and it is only applicable to small fish. In the end, research, experience and good old common sense should still reign supreme though.
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Old 08-17-2011, 11:30 PM   #5
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I remember my first fish tank when I was a kid.. it was a 10gal.. I think we had like 25 fish in there.. but back then it was not uncommon
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Old 08-17-2011, 11:58 PM   #6
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The inch/gallon rule works for small schoolers but that's about it. I stock (and give stocking advice) by visualizing the tank with the fish in it. If it looks crowded or incompatible then I start deducting stock till it works out.

It's a very culturally biased thing though, because in other parts of the world it is very common to cram lots of fish into a small tank.
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Old 08-18-2011, 12:18 AM   #7
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Thanks For the Feedback! Appreciate it :)

Quote:
Originally Posted by ilostnemo View Post
i use the inch per gallon rule but also know about those circumstances where it dont always work lol. like a 10 inch pirannha in a 10 gallon tank bs thats not happening lol. good write up!
Thanks! And definitely not, this is why it's not very good, how practical is it to keep pirhanas in ten gallon tanks?

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Originally Posted by adadkins1 View Post
AWESOME write up! I have seen so many newcomers swear by the inch per gallon rule. It is simply illogical. There is no way to have a rule that is set in stone pertaining to aquarium stocking, experince is a much better way to stock an aquarium.

There is no place for the inch per gallon rule in the aquarium hobby IMO.
Thanks!

Quote:
Originally Posted by absolutangel04 View Post
When I got my first aquarium, I started stocking by this rule, but then I revised my stock later. It is of course highly flawed, but it did give me a decent guideline to BEGIN with. Of course, the inch per gallon guideline only helps when people realize it is not concrete, and it is only applicable to small fish. In the end, research, experience and good old common sense should still reign supreme though.
Thanks! It does however have a few exceptions. For example, five ember tetras could do fine in a minimum tank size of five gallons

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Originally Posted by -=Jeff=- View Post
I remember my first fish tank when I was a kid.. it was a 10gal.. I think we had like 25 fish in there.. but back then it was not uncommon
I agree. Now we are all better informed, thanks to the Internet and some recent books and publications!

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Originally Posted by jetajockey View Post
The inch/gallon rule works for small schoolers but that's about it. I stock (and give stocking advice) by visualizing the tank with the fish in it. If it looks crowded or incompatible then I start deducting stock till it works out.

It's a very culturally biased thing though, because in other parts of the world it is very common to cram lots of fish into a small tank.
That is very true. Many stock based on what size the fish is NOW, not when it is fully-grown later.

Really? I had no idea! What countries or provinces? I have been to Mexico and parts of Asia, and so far the only problem I have seen in a fish tank was a dental office keeping an arowana in a 75 gallon tank.
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Old 08-18-2011, 12:45 AM   #8
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Quote:
Originally Posted by bruinsbro1997 View Post
Really? I had no idea! What countries or provinces? I have been to Mexico and parts of Asia, and so far the only problem I have seen in a fish tank was a dental office keeping an arowana in a 75 gallon tank.
It was just a generalism, but the family I have from overseas and other people that I know just treat the whole thing differently. I know to some people, certain fish are seen as good luck charms or whatever, and I've been into numerous asian restaurants with something like blood parrots packed in to a tank like sardines. The redeeming factor to it all is I get to bust out my famous line "Look at the bright side, at least they can help each other turn around."
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Old 08-18-2011, 01:14 AM   #9
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Awesome info. Thanks, I was told about that rule too and thankfully I've been reading enough to realize that, it's not just the size of either the tank or the fish, it's compatability and making sure they are happy and healthy. It's not about you being happy, it's about them.

Got to point out though............I forgot about the "full grown" size part. Thanks for the reminder. I have to stop forgetting that part when I'm researching what I want.
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Old 08-18-2011, 01:15 AM   #10
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P.S......It's not just for freshwater, it pertains to saltwater too
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