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Unfortunately, sometimes a clear explanation isn't available. We might guess as to why this happened and suddenly fixed itself, but you'd be left with 1/2 dozen guesses and no way of knowing what it really was. In my 20+ years of working on pools, there have been 20+ cases where I've ripped the system apart, found NOTHING that needed to be fixed and put it back together and the problem was gone... (My guess is that sometimes these things just want a little attention

Be thankful that your problem is gone but, if it occurs again, let us know and we'll help you.