Waterproofing a sensor?

Hi all,
I'm new to electronics and arduino/arduino programming, and my first project is a little ambitious - I want to have an arduino handle the maintenance of my fish tank, from switching a heater on and off to keep it at the right temperature, to feeding the fish and whatnot.
The reason I'm posting in this forum is that I'm hoping someone can tell me about the feasibility of waterproofing a thermistor, as well as the wires connecting it to the arduino. The rest of the project would be out of the water, except maybe a light sensor as well.
Thanks much, and best regards!
-Joe

This is the very first link that came up, when I googled "waterproof thermistor". It describes how to waterproof a thermistor for a fish tank, of course.

http://web.cecs.pdx.edu/~eas199/B/howto/thermistorProbe/

Encapsulate using hot glue.

This would seem to be what you want.
!(http://i.ebayimg.com/00/s/NTAwWDUwMA==/z/rn4AAOxy2YtRyGFz/$(KGrHqZ,!qgFGekKZpYsBRyGFzY!Tg~~60_12.JPG)
A digital sensor which you read with an Arduino, rather than mucking about with analog measurements and calibration.

Look for liquid electrical tape on eBay or at your local hardware store. It's pretty much made for this.

Thank you everyone. I'm going to check out these several solutions and find the best fit for my project. I already have a tinkerkit thermistor for arduino, so I believe I'll try and use hot glue and shrink-wrap to waterproof that. If the hot glue interferes with it's readings I'll probably buy that digital sensor.

Have a good one!
-Joe

jremington:
This is the very first link that came up, when I googled “waterproof thermistor”. It describes how to waterproof a thermistor for a fish tank, of course.

Fabrication of a Thermistor Probe

This looks pretty good but if you cut one leg to stagger the joints, you don’t even need the inner heatshrink tube. So you can use smaller diameters outer sleeve. If you also make the outer sleave the entire length of the probe lead. it produces a much neater appearance IMHO and one less place where water can ingress.

I have a number of miniature glass encapsulated thermistors that I have waterproofed for immersion in near-boiling water. I wanted a minimum of material so that the response time wasn't affected too greatly. After soldering thin wires to shortened leads I've been coating the leads and thermistor with a thin layer of JB Weld. It's cheap, easy to apply, non-toxic and an electrical insulator. It's probably not all that thermally conductive but I use a thin layer.

Here's an example. The tiny thermistor bead is at the very end.

edit: emphasis added

If this is for a fishtank, I would consider looking at buying a sensor that is made for the food industry.

No good if the system works great but poisons a tank of marine fish, could be an expensive and cruel experiment.