A month is too long to leave your tank unattended. Not only feeding but water levels and chemistry as well need to be monitored and adjusted. My lfs on the east coast of FL has a service where they will come in and take care of things. Don't know what the cost is, but it has to be less than replacing all the dead fish when you get back!! I would NOT recommend having a friend or neighbor taking care of them unless they are experienced with salt water tanks. Enjoy your vacation!!
several times i have had neighbors take care of my tanks from reef to aggressive. you just have to have a neighbor who is a good friend and leave detailed instructions. all of my friends know how important my tank is too me so they all think it is cool when i trust them. The only time when i screwed up was when i trusted my room mate. he had his own saltwater tank in the house but just let mine die out of sheer meanness. needless to say he is no longer a friend or a room mate. I also leave an emergency way to contact me incase things start to happen. that is alot easier if you are in country instead of out of country. but there are still was to do it. good luck
If your tank is only a 12G i would sell it, and start over when you come back if its bigger and worth alot of money hire a pro to take care of it, or else you whole system will be dead after a month.