Backyard Aquaponics
A place to discuss aquaponics

Give it a go... if it works great, if it doesn't not much lost...
you could make this smoother perhaps by filling at both ends and draining in the middle... makes less overall resistance for the water through your media.
but in practice it will probably not matter. I have no experience with super long beds, so can only speculate :-) perhaps 24' will work...