I disagree with both your points, Tom

"No, K+ will not raise pH, just like adding table salt, NaCl will
not raise pH either. To raise pH, you need a buffer, K+, is not a
buffer nor is NO3. KNO3 is a salt."

The comparison with NaCl is inappropriate in our context because
plants don't grab the Cl leaving the Na to oxidise and raise pH.
Plants/bacteria in healthy aquaria DO grab N from KNO3, leaving
K2O, which does raise pH.

"Better to use RO water to lower KH, than H2SO4, a rather nasty
strong acid, HCL, HNO3, may also be used, or peat. RO water is
the best solution and one used in most hobby tanks."

I presume that by RO you mean reverse-osmosis-purified water.
This is not acidic (except with CO2 dissolved after
purification), it's merely so soft that your plants won't get
most of their essential nutrients. (Unless of course you undo the
purification by adding aquatic fertilisers.) HCl is just as
strong an acid as H2SO4; HNO3 is broken down by biological action
in aquaria as above. All the pH-lower sold locally in fish stores
is dilute H2SO4.