It's because they are short and wide which makes them better suited to multiple tank setups. You can get more tanks in a space both lengthwise and heighthwise. Originally they were used primarily by stores and professional fish breeders for breeding/housing fish in large rack systems.
Like Andy said, enough footprint room to get busy but no wasted space height-wise. All the room is where it counts and maximizes surface area, vs. say the most worthless type of tank design, the hex, where most of the space is wasted in height.
how do you do multiple tank set ups in one tank? Dividers or slotted plexi-glass?
I get the footprint idea. Guess its why a 20 long is better than a 20 regular or 20 tall, or at least as it applies to cichlids. But it does make sense, and always wanted to know why they called it a "breeder". Maybe a 55 should be called a brothel...haha :lol:
I think they mean... since the tanks are shorter... it's easier to stack them 3 or 4 or more high...
To the right you can see my 3 tank Tiers of 50 br / 50 br / 75 gal on the left and right...
on the back wall you can see tiers of standard 30 gals (17" high as opposed to the 13" of my 50 br)... you can also see how it had to be several inches higher to allow for the same space between tanks (I like having ample space above the tanks).
Note : The bottom 30 gals are still missing supports beneath them which will raise them the couple inchesâ€¦ this will balance the distance above the bottom 30 gals to the distance above the 75 galsâ€¦