The Reef Angel open source aquarium controller has barely been out of the gate for a month and yet it is already gaining traction with third party developers. The new Reef Demon add-on is the first announced project to compliment the potentially disruptive open source Reef Angel. With a single pH probe and 3 temperature probes, you can tell that Reef Angel is being worked on by a reef aquarium hobbyist who is designing this system for himself as much as all of us. So what does Reef Demon do for the Reef Angel? So far it just controls temperature, to within an eighth of a degree, but if you want tighter temperature hysteresis than that, the curator of the Reef Demon add-on plans to get that range even lower. Roberto of Reef Angel should be getting cases for the Alpha run of the new open source controllers and we look forward to seeing this project gaining some momentum with more reefers/DIY developers. To keep track of the Reef Demon development, all the source code is being posted on github.