Water hardness\Discus? KH, PH, GH and GBH
 

I have returned to indoor fishkeeping after a few years break (About 15) Things are a little more scientific now :-? Can someone tell me if I can keep discus happily in my water.
I use a well filtered rain water with 1 ltr in 5 of boiled tap water (I am in a very hard water area) this gives me a PH of 6 - 6.4 the KH is 2 but GH is 12. My community tank with mostly tetra's and Angels with a few cribs and the usual array of catfishes seems very happy with no problems in this water. I am given to understand that Discus are a little more fussy about water qualities or am I just being paranoid.
I don't really want to go down the RO road if I can avoid it.
Any help or advice would be appreciated along with any information from Discus keepers using similar water to this.
Steve