for you basic SW
and fish if you buy a good quality salt for your water it will already have PH balancers and Calcium in it and should be all you need to worry about.
For the kind of tank you describe, here are the things you should always keep an eye on:
Nitrates: as close to 0 as you can get
you really only need a minimum of calcium in your water for LR
, as I stated above, if your using a good brand of salt it will already have calcium and PH buffers in it for you.