I"ve had severe problems with my
PH and
KH in the past but before trying to anything I needed to research...
I really need the info I asked for in detail to really get a idea.
Tank size?
PH before and after?
KH ------------------
GH ------------------
How much
CC added?
Substrate or filter?
How long before
PH spike?
7.5
PH is not really on the high-end, but the 1.5
PH jump can be very detrimental if sudden.
CC normally takes awhile and is gradual in its buffering of
PH,
KH and
GH, it generally has more effect on
KH which then affects
PH.
CC should be added gradually according to tank size, this step by step process normally takes weeks to achieve desired results.
It appears you may have other issues affecting your tank.
Never use untreated tapwater to do anything in the tank/filter, unless of course your tap comes from untreated wellwater...