Thanks Donald & Stefan for the clear information..
Too bad that I can not simulate the environment from where I purchased the cactus from, the seller is in a highland area where the weather is cooler and the cactus was grown inside a greenhouse, as compare to my current location that is very hot and the cactus kept in a balcony.
I'll try to move her to other cooler spot and hope she can adjust to her new environment, it is clear that the cactus is not happy now, the color is not shining..
There is also a problem with the issues in preventing the medium getting hot, as almost all of may cacti were kept in pot made from glass bottles, the glass get hot easily in direct sun, lets see how it goes.. Thanks again to all the Gurus here ...