GH vs. KH & pH levels

My tank:
37g, 5.5pH, KH 0ppm, GH 107ppm (according to Tetra test kit).

Water changes are done using distilled water 'fortified' with Aquarium
Pharmaceuticals "pH Adjuster" and "ElectroRight".  Needless to say, I can't
seem to raise my pH above 5.5 no matter how much pH Adjuster I add. I imagine
this has to do with the lack of KH. So, herein lie my questions:

1) What is the difference between KH and GH as according to the Tetra kit?

2) Which one more closely relates to the 'hardness' spec I read everywhere?

3) Instead of using the Aquarium Pharmaceuticals additives, what other
products (from Kent) would I use? (RO Right for hardness, Freshwater Trace
Elements for trace elements and ??? for pH)

4) What can I do in the mean time to raise my pH and KH?

I appreciate all replies!

Adam Aronson
aaronson at aol_com