I'm thinking that Randall's Goby may not do much sand sifting, assuming that is what you are looking for in the 29G. I have no experience with them but they are one of the prawn type gobies which typically do not sift sand. Others may have a better idea. In my 65, I have a Twin Spot Goby and a Rainsford Goby, both of which are constantly sifting sand looking for food. I spent a lot of time acclimating mine to accepting frozen food so that they were not reliant on just the sand bed for nutrition. Another good choice is the Diamond Goby but they can get fairly large and are jumpers, so I would recommend a good cover for the tank if you go that route!