What kind of lion and what kind of puffer is it? I'm assuming volitan and either a dogface or porky? The fish you currently have will eventually outgrow your 65, but depending on their current size, you could keep them for a pretty decent amount of time. Eels are always a good choice, and don't take up much room. Snowflakes, chainlinks, etc. are all good choices. Green wolf eels, although not a true eel also make very interesting tankmates. Do you plan on upgrading, or is this tank going to be it?