Ph testers and Ph probes are sensitive scientific equipment. They will require extra care and maintenance from the user (you) to ensure accurate readings, measurements and valid warranties. 

Ph testers (without replaceable probes) and Ph probes are electrical sensors and considered a consumable item. You should aim to be replacing these over time as you do media, nutrients, etc. Probes and Pens (without replaceable probes) only have a 6-month warranty from date of purchase and will not be honoured without receipt of purchase.

Probes and Pens with proper care can last for years, but as it is a live charge in the electrode it can be finished from 6 months. Moreso if correct care procedures have not been maintanined. Hydroponic nutrients in particular degrade Ph probes much faster than other disciplines.

Probes must always be rehydrated before use in storage solution, available for purchase in store

Probes must be kept in storage solution when not in use (in tank monitors excepted) 

DO NOT ALLOW THE PROBE TO DRY OUT AS THIS WILL SIGNIFACTLY REDUCE THE LIFESPAN