Ive never kept minnows but I would assume that 7 in a 29 should suffice. Itll no doubt be a better home that where they were at. If it really worries you get a 5gal bucket, any home improvement store has them. throw an air stone in there with some water from the tank you plan on putting them in. watch them for a week or two to a month. If their still alive and look good throw em in the tank. Assuming you have an air pump and a little air line tube it shouldnt cost more than 10 bucks for the bucket, air stone and maybe a splitter if your running the pump already in your 29. Or you can wing it and throw em in and cross your fingers