Before you put them in the same tank together, put the male in his tank and the female on another. Put them side to side and they will see eachother but not touch eachother yet. If the male sticks out his head fins or whatwver they are, he is ready, but sometimes, it means he wants to fight her. If the female is also sticking her head fins and her tail has vertical stripes, she is ready
I think it's when they stay low in the water where it is cooler. My basic understanding is they like it to be comfortable, just like humans. Nobody likes to sweat even if you're in water. The real question is what makes them better?