tap water & mash ph

Based on my Ward Labs analysis, I have very soft water with a pH of 7.2. My mashes have been very acidic (4.7 range). I have been testing my tap water with ph test strips today. The strips read on a scale of 4.6. to 6.2. They show my tap water as being very acidic ( less than 4.6). As a test, I boiled a cup of my tap water for ten minutes, cooled, and then re-tested it. It registered dark purple, above 6.2 pH.

I have also tested the pH of a cup of my tap water that I let sit out overnight. Still a pH of ~4.6

How is it possible that my tap water's ph can increase two full points after boiling? Is this a sign of temporary hardness?

I have been using a faucet charcoal block filter. I havn't been pre-boiling my mash water because I thought the filter would take care of it. But it looks like the filter is not the solution for my water.

Here is my water report:
http://ahomebrewlog.blogspot.com/search/label/water treatment

Any advise is much appreciated

I am sure there can be a couple reasons. One might be that boiling drives off CO2, CO2 in solution will drive the pH down. pH measurements are also temperature sensitive. I think most test strips are optimized for 20C (68F), hotter liquids will tend to make the pH read higher.

Also, pH of your water has little to do with the pH of the mash. The pH of the mash is controlled by the hardness of your water and the residual alkalinity in the mash. If you have water with low buffering capacity and are trying to brew something dark, this can drive the pH of the mash down, you should consider correcting with sodium or calcium carbonate.

I highly recommend the Brew Strong podcast dealing with water, John Palmer explains every aspects of brewing pH and making adjustments very well (4 shows):
Water I
Water II
Water III
Water IV