Im told Im to wait to put my new axolotl in his home, 7dys till condition works in water. why is this?

im told I am to wait to put my new little buddy axolotl in his home, 7 days to be exact until the water conditioning works. why would this be? I hav a filter running threw my tank about 8hrs a day. I also brought the Aloe Vera Stress Coat+ for condition... is this a good idea? I really want this to be a cosy and comfortable home for him, but can't work out why on earth a week. This pet shop assistant seemed a little to vague for my liking, just want to get it right.