For finding the right spot, I usually leave them somewhere and observe. If they start to lose color or PE, I might move them a little in one direction or another for a little while to see how they react. Info on certain named corals (like the bonsai) can be gotten from polling people. Different thigns work different ways for different people, so by comparing systems and responses, you can build an idea for whther it should go up or down int he tank, etc.
Alk is likely the most important level to keep constant (keeping it constant can help keep ca constant). Corals can live through low calcium for a lot longer than they can low or super high alk/dKH...