The module boards and sensor boards should last indefinitely barring damage.

pH sensor probes have a lifespan of two years and as such will need to be replaced.

Dissolved oxygen sensor probes have a lifespan of two years and require reconditioning every 3-6 months . They will also need to be replaced after their two year lifespan.

Electrical conductivity probes, temperature probes, and weather instrumentation will last indefinitely unless they are damaged.

You will also need to periodically recalibrate your sensors. Learn more: Recalibrating your Sensors