Originally posted by aquariumfishguy
What happens with extreme water temp differences is that (like others have said) it weakens the fish’s immune system to a point where any little issue that should arise could virtually spell disaster. Ick is one illness off the top of my head, which loves to attack a weak fish, and since the parasite is always among our fish in the water, your fish are bound to get it sooner or later, especially with a 7-10 degree temp change.
Well I must say that there is really no proof that ich is always in an aquarium. My aquariums have never seen ich. My fish have been moved on a 4 hour drive, had their aquarium heater stuck on til the temp reached 90F, been through varying temp water changes, had to deal with me rearranging the plants. I would have to sya they have been through stress and ich has never managed to rear its ugly head. I would therefore guess that there is no ich in my aquarium.