I'm in the woods pretty much. Someone came in and drilled a well for my place. My whole place is hooked up to it. I really hope my Ph isn't actually 5. I tested Publix bottled water. Same 5ph.... so maybe it's my GH solution. I went down a rabbit hole and I can't find a good PH pen. Bluelab is expensive and if it breaks you have to pay for shipping to get them to analyze it. I'm not trying to cut corners. But I also don't want to spend like 130$ on a pen.
You don't need to spend big on a pen to get accuracy. Even a cheap pen will work fine if you check calibration often and keep it in storage sol'n between uses. I trained as a a chemist so have kept my pH pen working OK for close to a decade now.
You're going to want pH4 and 7 calibration sol'ns. The pre-mixed liquid ones are what I use but many pens will come with some powdered salts you mix with water to make them. Get yourself some distilled water from a drug store to mix them with as tap water will almost certainly throw them off. Only 3 - $5/gal so not much. Follow the directions exactly to get it right.
Also get some storage sol'n to keep your pen in when not using. I keep a spray bottle with distilled or good RO water in it to rinse off the probe before and after use. Most pens have a cap you can put the storage sol'n in and sand the pen in an empty jar or cup to keep it upright.
If that bottled water also tested at 5 then it's got to be the test sol'n. That is never sold at low pH. Lemon juice is about 5 or lower.
The real pH of your well water is more likely close to 8 if anything. My dugout water which is also our tap water is pH8 and 400ppm depending on season. Just about to get diluted with spring runoff here so will drop to around pH 7.5 and 250 - 300ppm for a couple months.