One thing to keep in mind here................
Most fish available to the hobbyist are tank reared and are so far removed from their wild ancestors that it simply does not matter!!!!
There are a few exceptions...such as if you are breeding discus, but for the many tropicals available IMO there is no need to worry about adjusting the ph!!!
One should strive, however to provide as close a ph to the water the fish were in at the LFS. This, IMO is more important than worrying about what the fishes natural ph is in the wild where the fish has never been!!!
NOTE*.............when adjusting the ph, it is recommended to go no higher than 0.02 degrees per 24 hour period!!
CM