There's plenty out on the interwebs on pH for beer styles but it's tight...my reference is from Jamil Zainaschif (sp?) With dark beers being between 5.4 to to 5.6 and lighter, pales being 5.3 to 5.5 and additives like chalk and calcium carbonate moves you up towards 7 or neutral pH while calcium sulfate or gypsum moves it down towards 0. I think the ratio for using these additions is never more than a half teaspoon to a 5-6 gallon mash. So not a big space for "the sweet spot"!
There are paper pH strips for this range but a meter of course can be used. I think the paper is easier since it only takes a drop of cooled wort...I can do that off a spoon onto a cool plate in less than a minute....enough wort in a cup to read with a meter....not so fast! I have it on my brew day sheets but I don't sweat it if I missed that step but maybe you're way out of that range all together...worth a look if you never did...hell, brewers for thousands of years didn't know any better! Thank you Mr. Sorensen!
