A pomelo is closely related to a grapefruit. I had a difficult time finding store bought Pomelo juice so I juiced this myself from fresh pomelo's and it worked great! Just make note that fresh juice usually ferments faster that pasteurized juice. If you can't find pomelos, you can substitute grapefruit instead.
Make sure you use good bottles made for brewing. Check your bottles often by opening them so they don't explode.