Whether your keeping salt water fish or your planning a full blown reef aquarium it is important that your marine aquarium water parameters are in check.  For most reef aquaria and for salt water fish only tanks the parameters are as follows.

Calcium: 380-450 ppm

Alkalinity:  2.5-4 meq/L, 7-11 dKH

Salinity:  35ppt or a specific gravity of 1.024-1.026

Temperature: 77-83 F

pH: 7.8 – 8.3

Magnesium: 1250-1350ppm

Phosphate:  Should be undetectable

Ammonia, Nitrite, Nitrate: Should be undetectable, unless cycling.

  Constant testing will usually prevent and help any marine aquarium water problems.  Weekly water changes replaces used traced elements and keeps ammonia, nitrite and especially nitrate to near zero conditions as well as replaces calcium (if not already dosed).