TEST kits. Salifert recommended
water for top offs. These little tanks heat up pretty good, so you'll need regular top offs. Since the tank is small, the salinity levels raise pretty quickly.
Since it is a small tank, there is very little room for error. Most people think that small tanks are easier to care for thatn larger tanks, actually it's the opposite.
With less water volume, it is a much more volitile system. Some people have sumps/fuges larger than their nano itself. I had a very successful 12gal Nono with little problems, just need a little more TLC than larger tanks. Just as beautiful NTL.