first of all - you are running too hot!!!! 200 should be about the hottest you want to be!
clean radiator
clean it better than you did the first time!!!!
check belt on water pump if so equipped.
check for dirt around the shroud and fan blades.
check coolant level and type
check radiator cap
check with infrared thermometer to check accuracy of gauge!
now about that belt....
something does not look right at all.........
that spring should have a hellva lot more tension that it does in picture #3!
your belt is too long.......or wrapped around something incorrectly.
compare your old belt to new ???? SAME size? then your new belt is too big and will only get bigger over time as it wears.
I would not add another pulley - take the belt back and get one an inch shorter or whatever will place a good bit of tension on that idler pulley!