Honestly, I would never chase pH for any reason unless it's outside of 7.8-8.4. The other thing is I wouldn't recommend a buffer to fix any problem in a saltwater tank. You can get away with that in a freshwater system but in saltwater, when you added the buffer, the buffer probably affected your alk levels, which caused your SPS to die off.
If regular water changes worked well for you in the past, I'd stick with what works. As you continue to add SPS, you'll need to at least monitor your alk levels and make sure your water changes are keeping up with the usage of alk by the SPS. If at the point it isn't, then I'd look into additional supplementation of it.