Fishkeeping - RO and high pH

test

Brad T wrote:

I just started up a used RO unit, 3 stage at home...new carbon and
sediment filter. After letting about a gallon of water through the
system, I did a little testing, just to be curious. nitrate-0....my tap
water is 30mg/l
KH-none detected using titration method. The same true for
tap
pH-8.6 or....??? tap water reads around 6.8.
I just thought I would throw this bone to the learned crowd and see why
the pH is so high. I expected around 7.0. could the new carbon
cartridge be the cause of the high pH? I do not know how long the unit
was not in use before I got it, or if that would have anything to do
with it. My test kit for pH is fine..I tested it using distilled
water. I intend to retest the water tomorrow, to see if it is just a
startup thing.
Thank you.
Brad T