https://amzn.eu/d/eIGvMai
PH meters, cheap or expensive, add another level of complication with the need for calibration. I'd initially get a pack of these. Reliable, quick and accurate enough to identify if you have an issue or not.
Oats can reduce head retention, as can the high abv of a RIS. I'm wondering if the simplicity of the saison and other pales is the secret to their better head retention.
I'd think a simple course of action would be to brew an uncomplicated stout, with a grist of base malt and Roasted Barley and/or chocolate malt. Adding a teaspoon of calcium chloride to the mash and then measuring the pH.
Low pH actually aids head retention, so I'd hold off on increasing bicarbonate until you know what your mash pH is. Calcium on the other hand has many positive effects, and your source water is below what is recommended for most styles.
"Calcium (Ca++)
Calcium is a very important constituent and performs a number of functions:-
- Decreases the pH during mashing and wort boiling, favouring enzyme activity
- Promotes the precipitation of unwanted proteins in the kettle, hop back or whirlpool
- Promotes yeast flocculation at the end of fermentation
- Promotes head retention on beer
- Reacts with oxalate to form an insoluble salt, preventing gushing in beer"
Ionic Composition - Brewing Liquor - Murphy and Son