Oh my gosh! I was cleaning the fish aquarium yesterday we originally started out with little goldfish now they're huge. So I have to clean it more frequently. I drain the water out down to four inches just enough for the fish to swim. As I was hooking up the hose to fill it back up my son and my husband distracted me with something they were doing. I turned on the cold water and forgot to turn on the hot water so the fish would have warm water. I came back about five minutes later plenty of time before the aquarium was filled. I've seen the moisture on the side of the tank indicating how cold the water was. The fish was just barely moving. By adding hot water I balanced the temperature out. The next day the fish still seemed a little sluggish. I feel so bad I almost froze them.