I have researched, but found nothing like the outside mounted RV water tank level sensor like See Level has. I am looking to sense the water level in a fish tank, from the outside, and am using a PIC32 controller to drain and fill the tank via 12v solenoid valves. I want to monitor, as well as drain to a certain level, then fill to a level. My PIC32 is programmed on a timer to do this every other day. I am tired of relying on float valves. My turtle tends to disrupt it often.
Thanks!

 

Level measuring of liquids can be done by capacitive measurements. Check this one, http://electronics.stackexchange.com/questions/36614/precise-liquid-level-measurement-sensor .

 

Water level measurement can be done by pressure. The best unit is inches of water.