If urine represents what is being eliminated and saliva represents what is being kept, the PH of the saliva would be a better indicator of your PH and ideally this is what you should be concerned about. If you can keep your saliva at a PH of 7.0 and your urine stays at 5.8, I would not be too concerned. Eventually, I think the urine should automatically become more alkaline once you rebuild your alkaline mineral base. Also, are you keeping track of your urine and saliva PH several times over several days, then taking the average. If not, then you likely won't have an accurate picture.