The "inch per gallon rule" was derived back in the 1930s and 40s as a crutch for novices selecting mixed communities of small Platys, guppies, Tetras, Rasboras, and Barbs. The primary use, and only valid use, is for small, slender-bodied (flatten cyclindrical or cylindrical) fish less than 2" standard length. 1) Fish oxygen use and waste production goes up with body mass. Do you accept that? If so,2) body mass is not related to length, but closer to the cube of length, or more accurately to length and width and thickness. If you can believe that, you can see that the inch per gallon "rule" is effectively worthless. If you do not accept that, weigh and check the displacement (the two together will give you a mass index of each fish) of a variety of fish for yourself and you will find out the truth.
This also completely ignores the effects and requirements of aggresion, swimming space allowances, food competition, etc. It is based soley on mass, O2 needs, and waste production.
Beyond that, allowances must be calculated for the full adult size of the fish in question - calculations based on current size are as false as the so-called rule. There are many myth in this hobby. This is one of them and like most myths, leads the unaware into problems.
This also completely ignores the effects and requirements of aggresion, swimming space allowances, food competition, etc. It is based soley on mass, O2 needs, and waste production.
Beyond that, allowances must be calculated for the full adult size of the fish in question - calculations based on current size are as false as the so-called rule. There are many myth in this hobby. This is one of them and like most myths, leads the unaware into problems.
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