I thought a note on the [tag-ice]water parameters[/tag-ice] for seawater in a [tag-tec]reef aquarium[/tag-tec] might be useful, so here they are.
Please note that these are guideline numbers (apart from toxic items such as ammonia) – I can hear aquarists saying that theirs is different and their reef is fantastic!
Ammonia NH3 (toxic)
Nitrite NO2 (toxic)
Nitrate NO3 (nuisance algae nutrient)
10 ppm (parts per million) or less. As low as possible, better undetectable.
Phosphate PO4 (nuisance algae nutrient)
0.03 ppm or less. Undetectable is probably best. High phosphate can interfere with hard coral function.
pH (stable as possible)
8.2 to 8.4. (Note: the wider range of 8.0 to 8.4 is acceptable provided the measurement is stable. Some healthy reefs even run at 7.9.)
Alkalinity (‘buffer’) (stable as possible)
3.0 to 4.0 meq/l. (Can also be measured in dKH, multiply meq/l by 2.8. Thus dKH would be 8.4 to 11.2. There isn’t a need for such precision, so it can be 8.0 to 11.0. Seawater level is around 2.5 meq/l, the higher aquarium level is considered to be beneficial.
Temperature (stable as possible)
75 to 80 deg F (24 to 27 deg C).
Salinity (stable as possible)
This is measured in ppt (parts per thousand). However, here Specific Gravity (SG) is used as the majority of aquarists use this. The range that is recommended is 1.024 to 1.026. For a reef system the higher reading is possibly more advantageous.
Calcium (stable as possible)
400 to 480 ppm.
The above list represents the major test areas for a reef aquarium. There are other additives available, such as [tag-self]Iodine[/tag-self], but there is some controversy over the need for it, and others. when regular water changes are done.
(References: Borneham Eric. Aquarium Corals – Debelius Helmut/Baensch Hans. Marine Atlas.)