A pond with a volume of 30 gallons is going to be very unstable regarding its water condition I would have thought. What are its dimensions, did you really mean 30 gallons, is there a zero missing, can you go bigger, it would be of great benefit if you could?
Where will it be situated in regards to the sun as it will heat up tremendously being so small, that would'nt be very good for the fish. On the flip side, it will chill/freeze very easily too. Temp fluctuations as wide as what I suspect it will suffer aren't good for fish health really.
Have no idea where in the US you are, please do tell, maybe you don't get low temps, but then you could get high temps?