awc 2 optical level sensor redundancy

hi,

i have 2 optical level sensor setup for ato/awc. During auto water change, tank water would be drained past below the bottom sensor because it fails to recognize its dry state. This failure seem to happen around 1 year time to the bottom sensor. I suspect due to it being submerged all the time. I've had to replaced the bottom sensor about 3 times, each lasting about 1-2 year.

question:

1. would float sensor be more reliable to use as the bottom sensor ?

2. how can I use extra optical/float sensor for redundancy so that when the bottom sensor fails to recognize dry state and the water is drained past it, another sensor can stop the drain pump connected on the power bar ?

thank you