Don buy the PH tester in the photos they are dried out and defective. The units will not calibrate no matter how long you soak them. Freshwater sent me two bad units then moved them to clearance. BE AWARE there is no refund on clearance items. Horrible company who posted lies on google reviews saying I did not want to calibrate the tips which is untrue I've been using these testers for years and tried to calibrate these pens over 5 days they don't calibrate and don't even read the same in the same testing solution. They then said they did not move the ph testers to clearance again another bold lie look at the pics below. They do NOT GIVE REFUNDS on clearance items. Terrible customer service knowingly selling defective product with no chance of a refund. Stray away