Need advice on an appropriate level sensor

Hey!
I have a 15 gallon poly tank that is filled with a mixture of water and bleach. The concentration of bleach is high enough to corrode metal screws.
I want to monitor the level of the tank, accurately, via my network.
I was thinking of using an ultrasonic sensor( pointing down from the top) or an ir "sharp" sensor. I am concerned the fumes may, over time, corrode the electronics.
Any ideas?

They probably will affect the electronics.

You could use a tube and in the tube some floater (EPS?)
The floater sticks out of the tube and has some markers that can be counted or is connected to a potentiometer.

This way the distance between bleach and sensor is maximized.

Another possible solution could use the conductivity of the liquid - resistor array?

or a weight sensor under the storage?

maybe this - http://mechanical.poly.edu/faculty/vkapila/ME3484/Readings/NV27-Measuring%20Water%20Level.pdf -??

How about a toilet float hinged on a pot. Then analog read the position?