Nifty circuits wanted for aquarium

Hi, May I ask if anyone has or has links to nifty aquarium circuits? Something in the likes of Water level meters / switches, pH meters, etc. These should typicaly be submersible and if possible non-corrosive for marine tanks. Many thanks chris_t@telkomsa.net

I did a circuit, that if the temperature reached a certain level, fire an actuator arm to open a cabinet door (and let the heat out). The compressor generated a lot of heat, later 3 PC fans sovled the problem. But it was neat.

Imagine the cleaning crew cleaning art night and the door opening and no one is in the office.

Also, spray your circuits with (think it is called) conformal spray, but something to keep the salt off whatever you do make.