Review on Accurate and Reliable VIVOSUN Digital PH Tester Pen for Water Testing by Tony Reid

These meters work once calibrated, but like every other pH meter in the world, it needs to be calibrated regularly, rinsed thoroughly with reverse osmosis water after each use and stored in pH electrode storage solution. If you skip any of these steps, your meter will fail. A bottle of storage solution costs literally more than that meter, so do the math. Keeping all of the above in mind will give you a maximum of 1 year electrode life and being a cheap device is probably a lot less reliable. There's a reason real lab benches cost a lot more and the maintenance requirements remain the same. We replace the electrodes in the greenhouse every year in real use and properly maintain our devices.