Why would you want to? My guess is that the bioload would be much too heavy for a 29 gallon tank. When I started out in saltwater I had a 29 gallon tank and kept three fish in it. Eight would be way too much. Are these fish currently in fresh water? I realize that Mollies can be kept in saltwater if they are acclimated correctly, but with the cost of salt, etc., I don't understand the reason you would want to put them in salt. If I'm missing something here, please explain.