I found this out the hard way when I got a used set up and brought it home the SG
was way to high and I brought it down to fast. One fish made it the other didn't. I found out later what I should have done is basically drip acclimate it slowly with 2 airline hoses one going in and one going out and a fairly steady drip over a period of several hours or in my case days. The lady I got it from said her SG
was perfect it was at 1.025 when in reality it was at 1.052. I don't know if she was topping off with saltwater or not but at any rate she didn't know how to read a refractometer.
With the ph make sure there is enough surface movement because that effects the ph as well.