during the tank cycle, ammonia nitrite and nitrate are going to be what you're looking at. pretty much then on nitrate is going to me your main measure of water quality along with pH and a hydrometer to measure your salinity. (not a test kit I know, but still worth mentioning). If you're keeping corals, calcium and alkalinity will be ones you'll use often too. I rarely check the pH on my tanks anymore, as long as the calcium and alkalinity are staying constant... hth
- Misti
"Take care of the water; the fish will take care of themselves."