Why isnt it not possible? Machines malfunction all the time. If the swing was slow over those 4-5 days I wouldnt see a major problem, unless it went from 10 to 7 in a day and you didnt check it. But again, sps are picky and can STN at anytime. My tank's alk seems to love staying at 7 so i just leave it alone. I tried to keep it at 9-10 but it was a lot of work and kept wanting to swing back down to 7. I find that during the time you try to dial in alk some sps will lose tissue.