Aquaponic and hydroponic systems are growing in popularity. They provide a way to grow your own food, for yourself or for profit. However, they can be very time consuming, and not responding to a problem in time can result in the loss of your fish or plants. If you can monitor your systems better, or even have an automated system that can correct some problems, you can make your system more secure and prosperous. Arduinos are small computers on a circuit board that are very suitable for automating things. Unlike computers that have a keyboard, mouse, and display and are designed to input and output information, Arduinos are designed to observe and control physical objects. You can connect sensors to the Arduino inputs and relays or other devices to the outputs. You can then program the Arduino to perform various output actions based on the input. In this book, I explain ways that you can use Arduinos to monitor or automate your aquaponic or hydroponic garden. By monitor, I mean using it as a test instrument to report on conditions like water level, water and air temperature, pH, total dissolved solids, turbidity (cloudiness), etc. It is possible to sound alarms based on this information, display this information directly on a small screen connected to the Arduino, or even display information on a Web page. By automate, I mean actually act on the information directly. For example, it can monitor water levels and raise or lower water levels as necessary, monitor air or water temperature and turn on heaters or cooling systems, pump the water through a filter if it gets too cloudy, add chemicals to correct imbalances, and so on. I dedicate the first chapter of the book to a description of the very basics of Arduinos for those readers that are totally unfamiliar with them. I will describe what they are, how the set up the basic hardware and software you will need to use them, even where to buy them. In the following chapters, I will show you how to perform specific tasks with the Arduino, like creating timers for flooding and draining your systems that adjust themselves for temperature and humidity, maintaining proper water levels, maintaining proper air and water temperatures, monitoring pH and automatically adding chemicals to balance it when necessary, monitoring and reacting to total dissolved solids, turbidly, and so on. I will provide you with specific, usable code that you can load into the Arduino, and show you how to modify this code to make any adjustments you might need to match it to your system. If you are familiar with Arduinos, you will probably be able to greatly expand in the code I give you to develop very sophisticated systems. If you are not familiar with Arduinos, you will be able to simply install and use the code as-is, changing just a few numbers in the code as I will explain to make it fit your system. I will supply links to where you can download the code to save you typing long programs (called sketches).