RO water out of the tap, what are best products for conditioning and restoring kh?

Hi again. From what I can decipher from the products that I have, Kent RO Rite is comparable to SeaChem Equilibrium. I used the dose recommended for betas (soft water). It brought the dKH up to 7.
The API Proper pH 7 is a phosphate based buffer that prevents pH swings and stabilizes pH around 7. It's not one of those quick fix pH up or down products. It is similar to SeaChem's Neutral Regulator. I don't have a planted tank, so phosphate is not an issue. A tech at SeaChem had recommended adding Neutral Regulator when using Equilibrium. So, you think that I'm better off not adding the buffer and just stick with Equilibrium or RO Rite for my 5 gallon tank I'm cycling?
My issue at present (my betta's present holding tank) is that the substrate (or perhaps the silk plant which is attached to a white base that looks like stone) is slowly increasing the tank's pH between water changes. It is at pH 7.6 up from 7.2 a few days ago. Even after water changes it stays high.
The water that I am using for water changes is pH 6.4, which is too much of a pH swing. Even though I do a 25% water change slowly over a half hour and so far no problems, I am concerned about affect it is having on my betta.
The RO Rite doesn't change the pH. For the water change should I go ahead and add the pH buffer (API proper 7) to the water I'm using for water changes to bring the pH closer. It should also, if one can believe the product label, bring the tank pH down to 7 and keep it there. I didn't want to remove all the substrate in case I mess up what bacterial colonies I have established there.