Ive seen issues with sensative corals when raising it as slow as 0.5 dkH per day. After a few occurrences, i dropped my speed to 0.3 dkH per day, with no issues following.
Note: this is for emergency situations and major changes that are prolonged and at extreme values...and containing corals that are already stressed. (However, Alk will easily change by 1 dkH per day with no issues in many healthy tanks.) Each situation is unique, and there is great value in addressing issues fast. Use your knowledge to make your best judgement.