depends on the type of fish u have in the tank
if u have africian cichlids 8.0 is idle for them
but if u have a normal tropical tank u would prob want a more neutral ph (7.0)
do u condition ur water before u put it in the tank?
if you have a normal tropical tank i would recommend a product called bullseye 7.0 it takes the chlorine, chloramine out of the water it also makes the waters ph around 7.0