IMO the strips are useless. Invest in a decent handheld pH meter.
You can adjust your pH of the mash in two ways 1) via mineral additions 2) via acid/base additions
Mineral additions work by adding CaSO4, from which the Ca+ react with the wort to produce an acid and in turn lower the pH. Alternatively you can add chalk or baking soda to raise the pH.
The problem with this method is that adding mineral salts directly affects the mineral profile of the water and so the amount you can use will be dependant on the taste freshholds of those ions. If you are tailoring you water profile for taste than this method is counter productive.
Method 2 is to use an acid such a lactic or phosphoric. Lactic is limited by the same constraints are above, but phosphoric adds not flavour and as minimal impact on the mineral profile at the levels used to adjust the mash. Calcium hydroxide can be used in the same way to raise pH.
As from a practical stand point I can explain how I adjust my mash. I start my doughing in all my water except about 1 litres worth. I then take the pH with my pH meter (which I have calibrated before hand). When you take pH of hot liquids even though most pH meters (mine included) have auto temperature correction they will give a fairly inaccurate result at high temps. But I know from experience it will always read low by about 0.2-0.3 at mash temperatures, so I adjust my pH whilst hot to read 5.2. I do this by adding 88% phosphoric acid in 1ml aliquotes until I get the target pH. Then I complete the mash with the last volume of water, which I allows me to adjust for temperature loss during doughing in. I then retake the pH and do a final adjustment.
I then take an aliquot of the mash, cover the mash to keep warm and transfer the sample to the freezer. Once it reaches 20-25C I recalibrate the pH meter and take a reading. This is the final reading that goes in my log. If its way out (which it won't be) I can open up the tun and do a quick adjustment.
With this method I don't waste a lot of time at the pH adjustment step losing a lot of heat by pulling samples and cooling them. You can estimate the adjust required to same time with the number of additions using mEq calculations, but in reality you'll find after a few mashes that you always by adding a similar amount. In my case around 3 ml.
