This is one of those "Add Salt or Don't Add Salt" debates that could go on forever 
Certainly, any sudden change in water parameters can be stressful to a fish but I am inclined to believe that fish in the wild would experience a swing in temperature of at least a couple of degrees during the course of a day.
I also have had bad luck mixing hot water from my faucet with my tank. Your hot water lines in your house travel a different path than the cold. In many cases it leads to a hot water tank which can have scale and mineral deposits and who knows what else in it. In my case, using hot water lead to metals in my tank water that killed off invertebrates within a week of their introduction to the tank.
If you want to match temps (which is a good idea) I would suggest using cold water and letting it gas off in a bucket for a couple of days with a heater. If you know for a fact that your hot water lines/heater are clean as a whistle and don't contain anything sketchy, by all means disregard the previous two paragraphs
Certainly, any sudden change in water parameters can be stressful to a fish but I am inclined to believe that fish in the wild would experience a swing in temperature of at least a couple of degrees during the course of a day.
I also have had bad luck mixing hot water from my faucet with my tank. Your hot water lines in your house travel a different path than the cold. In many cases it leads to a hot water tank which can have scale and mineral deposits and who knows what else in it. In my case, using hot water lead to metals in my tank water that killed off invertebrates within a week of their introduction to the tank.
If you want to match temps (which is a good idea) I would suggest using cold water and letting it gas off in a bucket for a couple of days with a heater. If you know for a fact that your hot water lines/heater are clean as a whistle and don't contain anything sketchy, by all means disregard the previous two paragraphs
