"not much heat" he says
judging by the screen shot showing prices in AU$ I'm guessing you're in Australia, trust me on this you guys idea of "not to hot" is on a par with "sweet jeebus, I'm melting" for the rest of us, get a thermometer in there and go by what it says when it's at the top of canopy
it does look like heat damage, on my first round I just put my veg plants from CFL to HPS for flower and the older leaves did that before dying and needing to be removed, the plants were fine for it 31g from a exodus cheese and 45g from a liberty haze for first grow with a old HPS was pretty satisfactory
BTW PC fans are great for small localised air movement, handy in the setup i.e. 1 plant or high canopy on 2 plants, but for the love of jeebus get an oscillating fan in there pushing cold air from the cool unlit side of the room to the hot giant CFL side of the room
BTW maybe my own paranoia but might want to leave out photo's which identify you like tattoo's