I have a PH pen dilemma. Pen 1: Brand new Aphera PH 20 calibrated and reading 7 and 4 in solution. Pen2: Adwa AD12 calibrated and reading 7 and 4 in solution.
As soon as I put them in nutrient solution Aphera reads 6.1 and Adwa reads 5.8. Different nutrient solution Apera 5.6 Adwa 5.4. Tap...