Hi
@Northnut! Support your local growshop! First, this is country related, since we have various brands & models accross the globe. Next, your amazon pH pen is probably a cheap chinese crap, whereas you can find plenty of advices and reliable products at your local growshop. And in case you live in a place where there's absolutely no shop, I'm sure there's a good online growshop in your country! BlueLab is a good brand I can recommend, but not the cheapest. Hope this will help, happy growing! 👊