Can anyone helpI was given a fish tank - which I started setting up yesterday - the tank is 24 inches x 8 inches x 8 inches which gives a capacity of 5.5 gallons - but i have read on webpages in your link that you can one hold one fish per 10 gallons ie a half a fish.
I'm afraid that tank is far too small for goldfish. 25L or 5.5G is too small for most fish but possibly a few long finned White Cloud Mountain Minnows or (with a heater) a Siamese Fighting Fish. Even then its really half the size it should be for the long term.
Other than that, perhaps planted up as a nice shrimp tank?