For sophisticated reef tanks I recommend following parameters
Water temperature|25°C (24,5 .. 26) Salinity: |34,8 [psu] (34 .. 35,5) Density (at 25°C)|1,0232 [g/cm3] (1,022 .. 1,024) Spec. density (at 25°C)|1,0262 [g/cm3] (1,025 .. 1,027) Silicates 0 [mg/l] pH (in the morning)|8,2 Nutrients| Ammonium|0 [mg/l] Nitrites|0 [mg/l] Nitrates|2 [mg/l] (0,05 .. 10) Phosphate|0,05 [mg/l] (0,01 .. 0,1) Carbonate & Trace elements| Alkalinity/Carbonate hardness|7 [°dH] (6 ..9) Calcium |420 [mg/l] (400 ..450) Magnesium|1300 [mg/l] (1200 .. 1350) Following parameters are seen as critical| Water temperature|colder than 23°C, warmer than 28°C pH| for a longer period below 7,7 (in the morning) Ammonium|> 0,1 [mg/l] (toxic!) Nitrates|> 50 [mg/l] (Degeneration of small polyp stony corals) Phosphates|> 0,5 [mg/l] (Degeneration of small polyp stony corals)