Low KH/GH High PH

[Payin]

Hello
I’m using 100% RO water into my 200Gallons tank, 4 months since it was installed.
My water parameter with API testing and PH electronic pen are:
KH: 2
GH: 1-2
PH: 7.7 7.8
This parameter had been very stables since the beginning ( I think it is for the sand that buffer the ph, I don’t have any rocks) and I hadn’t have any problems with my fish, I introduce some tetra cardinals for testing and no problem so far.
So, my question and thank you in advance, I want to have a lot of tetra cardinals (from breeders not wild caught) and obviously maybe 10 hybrid discus, do I need to worry about my High PH? , or I continue as I have doing so far with stable parameters.
thanks

[broadfoot]

As long as it's stable (as you say it is), discus can handle that kind of pH. You'll need to acclimatise them carefully, and gradually get them used to the pH (which will probably be higher than the water they come to you in). Fish can handle dropping pH more comfortably than rising pH. You might want to google around for some rates of change that they can handle, and measure the pH in the bag that they come in.