Depending on what dechlorinator you use, yes. However, I heard that with Stress Coat +, you need to put something like 5 times the recommended dose before the fish start even noticing it. I'd imagine its the same for other brands as well.
I would think the amount would depend on the situation. if you barely have enough oxygenation for the fish on a regular basis, it won't take as much as if you had a tank that was O2 saturated.
I would think the warmer the water, the less you'd need before seeing problems.