Let's not get crazy here, don't go putting mandarins in too small of a tank. 29 is alright, 24, meh, no smaller IMO. Any smaller would probably make them feel like they were in jail. My tiny mandy is ALL OVER my 75. Not the police, but it's better to be able to keep one successfully without praying for it to eat frozen. PLEASE know that you may end up buying live foods for these animals, and the above mentioned advice is great, but unless you follow the advice given, you'll just end up killing fish.

Sorry, I have a thing for mandarins...