The friendliest place on the web for anyone with an interest in aquariums or fish keeping!
If you have answers, please help by responding to the unanswered posts.
Offer to talk to the owner about it. If you want substrate I would do small gravel. Goldfish don't mind it and you can use a gravel vacuum all you want on it.
Exactly, the cafe folks don't know and many of the customers won't. Ask if they would be willing to invest in more proper equipment and that you would be interested in helping them out. It would be a great chance to help out and get more people educated... seems like PR gold to me...