Hi Pam, I've been crabbing since January, too. The footprint of the tank is the length x width. This determines the surface area or what I call "square inches on the ground". The volume or gallons a tank can hold is calculated length x width x height, and different tanks can have the same volume but different dimensions. So you can have a "20 high" tank that measures approximately 24L x 12W x 16H; a "20 extra high" that measures 20 x 10 x 24; and a "20 long" at 30L x 12W x 12H, all of which hold 20 gallons. Of the three, the 20L has the "long footprint".crabbyjo wrote:What do you mean by long footprint?
For crabbers the priority is surface area, to allow more room for digging. A 20L has 360 sq. inches on the ground, while a 20 high has 288. The 20L is only 12 inches high, so keep in mind that when you put 6" of substrate in there, you'll have 6" above the ground... just like you do with your 10 gallon, so you already know what that looks like. A 29 gallon tank has the EXACT same footprint as a 20L, but is taller (18"), so you gain no advantage in terms of surface area, but more height if you want to decorate and have climbing areas.
I've been researching what size tank I want next pretty intensely (I have a very small house!), so I'm just passing on what I'm learning! Hope it helps.
P.S. If you have a Petco near you, they are currently having a "dollar per gallon" sale, which means you can pick up a tank a lot cheaper than regular prices you'll probably find at Petsmart. Right now the 20g at my Petsmart is around $32, while the Petco sale is $20.