I would recommend Instant Ocean Salt. The purple box. It is inexpensive and gives great results without the over-addition of elements. I suggest getting a new test kit if your going to be serious about keeping a reef. API will get you started, but seems to get more and more inaccurate as you use it and it ages. RedSea makes a great kit for the basic elements, and a good kit for Nitrate. If you have nitrates, generally your Ammonia and Nitrites are going to be Zero unless your adding something uncured to the tank, such as live rock that's dead, but was once live.
Here are a few to look at.
RedSea Nitrate Pro Kit
Red Sea Reef Foundation Pro Ca/Alk/Mg Multi Test Kit
These two are worth every penny and i keep a very successful SPS
Dominate Reef with them.
I use the purple regular Instant Ocean Salt mix, and I add calcium and alkalinity suppliments as needed using these REEF Products:
Seachem Reef Fusion Two Part System 1 & 2 Calcium and Carbonate Supplement - 4 Liter each
Now, There are smaller bottle available, I just buy these ones because I intend to use a lot of it. I do not have automatic dosers, so these work great for me. As you can see, my tank is about 7-8 months old, and im just starting to grow the coraline. So be patient, and you will be rewarded.