When you add a discrete video card that has a fan on it you will notice that the bracket end of the card has a series of vent holes. The heat that the video card generates is vented out that bracket end of the card. Because of this the temps should go down and not increase. There are of course a lot of different video cards and some of the ones with the dual fans don't blow the heat out the end it blows the heat off of the card into the case so the internal case temps increase if you don't have sufficient case fans for ventilation. You could look at the case fans layout and see if you can add or rearrange or change the size of a few , but the key would be to optimize the case fan ventilation.