Some fish can handle a pretty big change in pH when acclimating as long as it is done slowly. I recently bought 4 small striped angels for my 75 gallon. When I got them home, I tested the bag water pH as well as that of my Q-tank. The Q-tank was 7.0 but the bag water was as low on the chart as it goes, 6.0 or lower. Not having much choide but to try to work it out, I started adding 6 oz of tank water to the bag every 10 minutes. It took 40 or 50 minutes before the bag pH even moved. I spent 3 hours doing this (pouring water from the bag into the tank when the bag got full) before I had raised pH to the same as the tank. I know that was a huge change in a 3 hr period (would have spent longer but didn't get home from LFS till about 9:30 PM so it was about 12:30 when I finally put them in the tank) but it worked out as the angels are now in the 75 gallon and doing fine. One thing I would advise everyone to do is definitely check the pH of the bag water from the LFS before you start the acclimation so you know what kind of change the fish are getting ready to go through and how much time you need to spend.
