mixing RO water and tap water

[m1nh0h]

is there some kind of formula with mixing a certain amount of RO water set at a certain ph with mixing tap water set at a certain ph, it seems like adding tap water affects the water more so than the RO affecting the water

i've been using API liquid ph test kit, should i get another kind??

[Northwoods Discus]

Do I follow what you are trying to ask, why does Ph change so dramatically with a small amount of tap added to the R/O? It is due to the fact that R/O has no buffer capacity, no minerals to absorb the hydrogen (acid) or OH (basic) when the tap is added. It depends on the Ph and hardness of the tap that is added.

[m1nh0h]

ohh okay, yeah u answered my question, thanks!