But if you are just adding the fish to the tank water with out a proper acclimation this is stressing the fish a lot, especially since the water qualities are obviously way different. Floating the bag for 25 moniutes accomplishes nothing. A true acclimation can take an hour depending on the fish and has little to do with matching temperatures.
In my tank I place the new fish in a small container (tupperware etc...) with the fish store water. I then start adding water from the tank into the tupperware. A little at a time over the next hour to 2 hours. This slowly gets the fish used to a change in water quality. When the container starts gettign full I take some water out of it and eventually the tupperware will be mostly filled with tank water. Then scoop the fish out with a net and add it to the tank.
You still haven't mentioned what the water source is and what chemicals you are adding to the water.