AquaLog

Aqualog is a Microsoft Windows application that can be used to monitor and log any number of marine, reef, or freshwater aquariums.

It is designed for both hobbyist and professional use, providing a convenient way to track water test results, maintenance items (such as water changes and chemical additions), and to keep an annotated log of observations.
AquaLog is Open Source. You can download the fully functional version below. You do not have to register, give out your email address, or send any money to use it. However, If you do find it useful, please consider a $5 donation to help fund my website and support future software development.