BillieBricks:
Great link to you tube you just gave me. I found the principle of fault tolerance in the float switches combined with the pH probe quite interesting...
I did implement an auto top-off function in my device, but this is just to make sure the nutrient tank doesn't become dry and kills the pump...
In my case I was also worried about the pump burning out (I don't know how likely this actually is, but better safe than sorry) and so i placed my lower float switch slightly above the water level where the pump sucks air and use that float switch to turn on and off my pump.
One thing that i have been thinking about as a precautionary measure. Is to measure the amount of time it takes to top off my tank from its low position to full position when water is at its maximum pressure. So if it takes 5 minutes to fill tank say
if lower float switch is low
turn on water
reset timer to 0
start timer
else if higher float switch is high or time exceeds 5 minutes
turn off water
Can you post your latest code?
Are you still having problems with the calibration of your pH meter?
Did you have to calibrate your temp/humidity sensor?