If you can get hold of Sodium Bicarbonate powder, put it in your bath water and soak yourself for an hour daily. If not, half hour twice a day. You can also add some Epsom Salt to your bath water, magnesium in ES is very helpful in many reactions in your body.
I know that during a water fast, your thyroid becomes hypo, one possible reason why your bicarbonate level may be low. Another reason is dehydration, taking certain drugs and even while drawing blood if the nurse keeps the rubber band on your arm too long. Did you take any drugs before and during your fast?
I don't think you need to worry as long as you are hydrating your self well. Alkaline Water is fine.
After you complete your fast you may want to contact Dr. Sircus.