Is the 1 inch per gallon rule reliable for a 20 gallon tropical tank?

-Does this rule cover all areas of the tank (top, middle and bottom dwellers) and does it include the tail fin because it is so thin? Is it good to use when stocking my tank? If not, is there a better thumb rule and how does it work?The "1 inch per gallon" rule is pure garbage for any size of tank.

Please do yourself a favor and forget you ever heard it.

The same is true of any other "rule" that mentions gallons and inches (or centimeters and liters, for that matter).



There's really no all-purpose rule for tank stocking, because the needs of each species are different. You have to take into account not only the body size of the fish, but also the activity level, oxygen requirements, territorial behavior, and (we hope) breeding patterns of each species. So the winning strategy is to learn as much as you can about the fish species you are considering (before you get the fish, not when you already have it), and plan accordingly.



Even if the one-inch-per-gallon myth were true for one-inch-long fish, it would not be true for larger fish. You might be able to keep 10 one-inch fish in a 10-gallon tank (in fact, often you can), but that doesn't mean you could keep 2 five-inch fish or 1 ten-inch fish in that tank. The mass of a fish's body (and therefore the bioload on the tank) increases roughly with the square of the length. That means that a two-inch fish is not two times as big as a one-inch fish; it is four (two squared) times as big. And a five-inch fish is 25 times as big, and a ten-inch fish is 100 times as big, as a one-inch fish. Not to mention that fish need swimming room, and that you have to be able to filter the tank sufficiently without causing so much water movement you batter the fish to death.



Having said there are no all-purpose rules, I will now give you two:

1. Always plan based on the maximum adult size of a fish you're thinking of getting-- not based on the size it is when you get it.

2. Only put half as many fish in your tank as you were thinking of.No. It's a very outdated rule and isn't used very much anymore.

I would suggest staying away from it all together.



The only thing I can advise you with is to look at the adult size of the fish and find the minimum tank size they should be kept in. Obviously some wouldn't work by just looking at adult size...like a common pleco which can get over a foot long. Would that work in a 20 gallon heck no. How about a some tetras who only get to 2-3 inches? Yes in this case it would work.



Just always do your research ahead of time.



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It's not reliable for any tank, and there really aren't any rules of thumb to go by either. The best thing to do is put together something you want, and have knowledgeable fishkeepers look it over and make changes as necessary.
http://aqadvisor.com/

This should help.
I tend to use 1cm per litre and it does exclude the tail.