I'll second the finding a rotary processor idea. However, I had great success with the fish tank heater method. The fish tank heater is kinda tricky though. I went through several until I figured out how to avoid the huge temperature flucuations. I ended up with the cheapest heater that the local petsmart had. My guess was that the more powerful heaters I had been purchasing couldn't turn on and off fast enough with my small volume of water. Thus, I suggest if you go this route, that you use exactly the volume of water suggested by the fish tank heater manufacturer. Getting the next size larger will kill fish and film.