Loosing sleep over this

hello everyone,
this is my second attempt at growing and im having a slight problem..some 2 of my 4 plants have some crisp yellowing...on another one the first leaves from the bottom are yellowing but arent crispy...might just be a light burn but i need to know...

http://img86.imageshack.us/img86/588...e010ce9.th.jpg

hard to tell from tiny pic
low leaves yellowing cant be from light burn
i see evidence of heat stress my first guess is that your temps are getting into the high 90s regularly
my second guess is that your soil is not the right pH
better pics please and monitor your temps