ok i found out that my gf tank is ok now we got her ph down to 7,2 anywho her tab water is 8.7 . Now i have been giving her my tab water and bring the ph to a 7.0 . She dosent put the water right away in the tank and im wondering if thats bad, question 2 or should she buy a acid buffer?

Start using R/O water. This will help level out your ph and is much cleaner than the water from your tap.

Chasing a Ph with a buffer is pointless IMO. I'm not sure where your located but we get our R/O water from our local super walmart for 33 cents a gallon.
Also driftwood will help bring down a Ph.

Reverse Osmosis filtration. It's the most pure water you can get.
Snowboss had algae like crazy in his saltwater tank once he switched to R/O water it's been clear ever since.
Tap water has impurities already present in it because theres no crazy filtration going on. And depending on where you live like a city or in the country with your own well the Ph will be different.
I think R/O water is pretty neutral.