[Blue Blade Fish] wanted to build an Arduino-based aquarium controller. He’s detailed the system in (so far) 14 videos and it looks solid. This isn’t just a simple controller, either.

Arduino, myDevices “Automation At Home” Contest Winner Crowned at Maker Faire Bay AreaThirty IoT Projects Submitted Including Winning Smart Aquarium ...

But Arduino enthusiasts don’t have to look far to find offerings like this PAR meter build, or this aquarium light controller library which can be recreated using the ubiquitous controller board.