just do your weekly water changes and make the water you're changing the salinity you want the tank to eventually be and continue doing that until your tank salinity is at the level you desire. That's what was recommended to me in order to keep the freshwater bacteria alive and cultivate some saltwater bacteria as well. Then also check this forum out it discusses it as well: http/www.fishforums.net/index.php?showtopic=69385&hl=