a giant would be fine in a 5 gallon, but would be even better in a 10. plus if he's not too aggressive, you might just have room for a few tankmates (a trio of not-too-bright platies could be a good option)
So remember, when you're feeling very small and insecure,
How amazingly unlikely is your birth,
And pray that there's intelligent life somewhere up in space,
'Cause there's bugger-all down here on Earth.
Loki/Grendel/Gail/Beowulf/Camilla/River/Bathory/Arwen/Lafayette/Deb/Jack Skellington (soon)