A few days ago, based on the recommendation from a friend, I downloaded Aquaplanner to my iPhone. It is a great app and only cost $2.99. This app has a lot of features for tracking and logging information about your reef tank. What attracted me to it initially was having the ability to track water tests. It has a very intuitive interface and works very much like the standard Apple apps. You can track livestock, equipment purchases, water parameters and more on multiple tanks. It will generate graphs and help you keep track of things. I highly recommend this app. And you can't beat the price.