and another one to automatically shut off the pump as a fail safe
However, if you do use the arduino, I would recommend adding in another fail-safe to prevent the pump from running too long, in case one of the switches fails in a 'low water' state, and makes the pump over-flow the tank when you aren't looking.
Quoteand another one to automatically shut off the pump as a fail safeI would use this to disconnect the pumps power directly i.e. not fed to the Arduino.
Is there any reason for the Arduino to be involved in the pump control, if it's ultimately going to be triggered by switches anyway?
I don't know anything about keeping fish or reef systems, but I'm surprised that it isn't possible to get a reliable float switch
What are the capacitive sensing ones that go on the OUTSIDE of the tank?
I dont know if the water level tape would work with salt water so i would have to research that. I also would have to worry about corrosion and calcium build up on it as well.
I was thinking of having the float switch turn the pump on and keep it on for like 30 or so seconds and then start the loop over again. Otherwise i think it would constantly going on and off. This will also help keep the salinity at an almost constant value instead of waiting until the system absolutely needs water and then adding two gallons of fresh at a time.
for an extra measure of safety i was thinking of having a float switch at the highest point of water acceptable. like a few inches above the normal so it would at most only add an extra gallon or two.