I think it's worth mentioning that with a 29 gal you're much better off with a small species like the dwarf Indian mudskippers. Large 'skippers like Africans (the most common) are aggressive and would probably outgrow that tank. With dwarves, you could probably have more than one. I'd say 4 or 5 for that tank max, and make sure there are multiple places on land for them to claim territory.
Also, as with most gobies, it's best that you use a fine sand substrate, to avoid damaging their soft skin or fins. They'll probably want to burrow, so something they can dig in is best.