I am sorry but I do have to disagree that a mandrin cant live in that 29 gallon. I have a 30 gallon and I have a mandrin in it and it is doing just fine. As far as I know it does not eat frozen food at all, I did try to find one but all the ones that I looked at didnt want to eat it. Mine has been living off the pods in my tank for 7 months. Very fat and happy. My suggestion for the tank is to get a whole bunch of little LR and make a layer with it across the back of the tank, You can hide it with bigger rock if you dont like the way that it looks. I didnt like the way that it looked so I put bigger rocks around the layer so that you couldnt see it. That layer of rock will serve as a breeding ground for the pods. The common amount off rock is 1 lb per gallon just make sure that you have every bit of that in the tank and maybe a little more. It is possible to do it. If you ever get scared that there arent enough in the tank then you can always try to find a LFS that sells them or order them online to put in the tank.
Whatever you do good luck to you and I hope that it all works out.