About 20 years ago, I was at my parent's place, and cleaning out the goldfish tank that I'd left when I moved out and up to the power stations. Drained about 2/3 of the water out, when my SIL came into the room and asked what I was doing. I replied that I wanted to move my fish to my new location. So being on holidays for a fortnight, I've taken out half the water today. Tomorrow, I'd take out half the remaining water. Next day half of what's left, and by the time my holidays were over, the fish would be comfortable on the gravel layer. I would place said fish in a shoebox, and take it home with me and set up the tank in my home. First day home, I'd tip in a tablespoon of water. Next day two tablespoons, next day 4, then 8, slowly getting the fish used to being back in the water... She walked away satisfied, and about 5 minutes later, my brother burst through the door laughing, and complaining that I should have at least waited until he was in the room to explain how to move a fish.