Reddit reviews Acid Testing Kit

I use one of these -

https://www.amazon.com/Midwest-Homebrewing-and-Winemaking-Supplies/dp/B0064OFUCY/ref=sr_1_3?keywords=acid+test+kit+wine&qid=1556626594&s=gateway&sr=8-3

Ugh, sorry - I use the technique they hid in the details
"A pH of 8.2 is also where a titration dye, phenolphthalein, changes color". It's definitely true that a GOOD ph meter will measure 8.2 more reliably than phenolphthalein, but mine is decidedly not a good one lol (I should really upgrade but they're such a pain). In either case it's generally true that measuring TA is more closely correlated to perceived sourness than PH so its a useful metric for deciding "sour enough" or at least "repeatable perception".

We bought one of these kits (from a local hbs but link for clarity) https://www.amazon.com/Midwest-Homebrewing-and-Winemaking-Supplies/dp/B0064OFUCY which has both the indicator and the 0.2N sodium hydroxide (note that that is 2x what most ppl are using for beer which is 0.1N - you can just use 1/2 as much -i.e. 1ml instead of 2ml or dilute 2:1 with distilled water - the latter will give more accurate readings).

The default setup for that kit is to measure acidity as tartaric so you have to do a slightly different calculation - basically take the calculation that comes with the kit and multiple the result by 1.2 to account for the different density of tartaric vs lactic.

If you work out the math the wort density is pretty much something you can just ignore (yeah it moves it a fraction of a point but.. whatever) especially if you're mostly controlling for "repeatable perception" on similar wort bases. The FG will have a dramatic impact on perception (sour beer == sweet/sour balance) so its worth taking into account in that regard but doesn't change measured acidity meaningfully.

Note also that different acids perceive dramatically different. Plantarum is good for producing very clean lactic, but if you're using something that produces acetic or other acids you can't strictly compare the perception 1:1 with a straight lactic ferment based on a simple analysis like this (or ph). Remember if you can smell the acidity using only your nose there's likely acetic in there (or some other funk your brain is translating as "sour").

They are ok for PH but acid level is a different animal. Google titration or "acid test" kits.

http://www.amazon.com/Midwest-Homebrewing-and-Winemaking-Supplies/dp/B0064OFUCY