What is the origin of the 1 inch per gallon rule?

[reberly]

I've been wondering what this formula is based on. I assume aeration, tank shape, water quality, upkeep, filtration and such would make a big difference. I seem to remember reading somewhere that higher aeration allowed for more fish. Is the 1 inch per gallon based on the amount of room they need to swim and be happy or is it more scientific such as the amount of waste an aquarium can effectively handle? I just remember my best friend's tank back in grade school. He had a 10 gallon tank with a one of those crappy in-the-tank corner filters and a couple airstones. He had at least 2 dozen assorted fish in that tank and they not only survived, they THRIVED. He lost MAYBE a couple fish a year, the rest were happy, even breeding every so often. He had to GIVE fish away cause he had too many. It was insane, of course he used to do crazy stuff like washing things in bleach and doing massive (50-60%) water changes every week or two. I never figured out what his secret was, but he was a fishkeeping master. Sorry, I'm rambling, I'll stop now. 8)

[fishfreek]

Im not overyly sure myself as it was a 'rule of thumb' (i would not call it a rule) well before I got into the hobby.

I think it has to do with oxygen takup by the fish, waste production by the fish and the ability for the water volume to dilute the fish waste enough so that the bactera living in the substrate can process it.

Ideally if you have more surface area you can have more fish for the same volume. So a 20 Long is better than a 20 High because you get more surface area. Greater surface area means more substrate to hold bactera and it also means higher gas exchange.

for your friend doing the massive water changes reguallry probably was one of his secrets. This would maintain water quality to some degree since he we diluting the dirty water by 1/2 on a regular schedule. Cleaning things with bleach would be fine since it would sanatize them. I doubt he bleached the substrate on a regular basis and thats where the bulk of the bactera live.

Also note that for lets say a 10 gal tank 1 10" fish is not the same as 10 1" fish. The larger the fish the more waste is produced. Plus a larger fish in a smaller box would cause more overall stress on the fish because of its cramped enviorment.

[shawmutt]

I assume (and we know what THAT does ) that some lfs got sick and tired of answering the age old question of aquarium addicts everywhere and came up with this formula to shut them up. Unfortunately, like every other oversimplified formula, it stuck and became a "rule of thumb." My cichlid book says for cichlids there should be 2 1/2 Gallons for every inch of fish...and just try to fit one inch of goldfish for each gallon of water 8O . It really depends on the fish.