Interpreting water hardness test results

[Yenko]

I just did a set of water tests on my aquarium.
PH: 7.2 (trying to lower it with peat moss)
GH: 60 ppm (Hagen test kit)
KH: 90 ppm (Hagen test kit)

How do I convert this into DGH and DKH?
Does my high KH measurement mean lack CO2 is raising my PH (Aquarium is well planted, and most plants do well in it)?
My PH normally goes from 6.9 to 7.1 in the course of a day because of CO2 depletion from plants.
I don't have a CO2 injector; I've only got 40w of lighting in the tank.

 

[Morrgan]

According to the book Practical Fishkeeping by Mary Bailey and Gina Sandford, these are the conversions:

1 English or Clark degree of hardness = 14.3 ppm
1 French = 10.0 ppm
1 American = 17.1 ppm
1 German = 17.9 ppm

There's also a note in the book that English, French and American degrees measure CaCO3, while the German measures CaO.

I assume it's the German you want? I think that's the one that's usually used in fish books, but don't take my word for it.