Question about RO/DI water???


I have a RO/DI unit and when I do water changes I add the salt and it buffers the water to around PH 8.0 and KH 10. And a little super buffer dkh will get it just right. But what about using the RO/DI for topping off the evaporated water? The plain RO/DI water has 0 KH and the PH is 5.0. Do I need to buffer it with anything or just add it like it is? I'm thinking I would just add it and it would be fine, but didn't want to chance it. Can anybody help me out??