Liquid pH indicator is fine- you said you have some?
B. subtilis is a species of bacteria that is an active component of a bunch of different products. I'm not sure what other names are hang on one sec google time.
Bacillus subtilis - Wikipedia, the free encyclopedia <-there's the stuff
Check out Botanicare Hydroguard. It's actually a couple different varieties of bacillus and was developed for use on .... CANNABIS! Whooo hoo!
I promise I'm not a hort genius. Just an evil genius.
Get the space heater AWAY from the plant. Hang it from the ceiling, turn it pointing away from the palnts, ANYHTING so it does not blow right on them. The pic does look like a plant that has been exposed to really arid conditions- the leaf-edge curl indicates drying.