RTN is unfortunately fatal, as it happens very quickly. Maybe you are experiencing STN, which is much slower.
Get some buffered Vitamin C (Sodium Ascorbate), and dose according to this regimen:
http://blog.fragd.it/2009/05/21/dosi...ium-ascorbate/
The last thing you want to do is give the sps more temperature swings. Get a controller that turns fans on when the temps get above 81'. That is how I battle the heat.