Introducing fish from diff pH

[Daid]

Hi,

My tanks have cycled
pH: 7.6-7.8
NH3: 0ppm
NO2: 0ppm
NO3: 10ppm

Currently with 6 guppies.

The pH from the LFS is about 7.2-7.4. How would i introduce new fish from the LFS into my tanks without having them get fin clamp or pH shock.

I know about floating the bag in the tank and slowly adding water, but is that enough? I've had fish get sick/die even when i do this.

Cheers