IMO the best way that has worked for me in acclimating natives to tropical temps is to set up a tiny holding tank for a day. and have it at room temp. then acclimate them into the holding tanks temp. after tehy are acclimated, wait a few hours then throw a heater in, slowly raise the temp to the tropical temp as they should be fine.
Fish acclimating from cold to warm seem to stress more than warm to cold.
