Ron Shimek's Website...Critters
"Coral reefs are generally located in areas that have salinities in the range of 35 ppt to 38 ppt. Most of our corals, and the associated fauna including fishes, will live best at those conditions (Weber and White 1976). Most organisms, even osmoconformers, can survive for brief periods in salinities well outside their normal range. But if maintained for longer period outside of that range they will be stressed and eventually will become so damaged that they will die even if returned to their normal salinity. Higher salinity is slightly more tolerable to these animals than is lower salinity, and adult animals are more able to withstand the extremes than are the juveniles or larvae."
"The bottom line for salinities is simple. There is simply no reason at all to maintain the salinities of our systems below normal reef conditions. All reef inhabitants will suffer damage from prolonged exposure to lowered salinities. Invertebrates kept at low salinities often die within a few days to a few months. Given that corals, sea anemones, sponges and some other invertebrates have no old age or senescence (or to put it another way, they are immortal), low salinities result in a quick death. Some mollusks, crustaceans, and most fish kept at low salinities die of kidney failure; it just takes them longer. A fish which dies in a couple of years in a hyposaline aquarium may have had the potential to live more than 20 years had the salinity been appropriate."
Reef Aquarium Water Parameters by Randy Holmes-Farley - Reefkeeping.com
"For reference, natural ocean water
has a salinity of about 35 ppt, corresponding to a specific gravity of about 1.0264 and a conductivity of 53 mS/cm.
As far as I know, there is little real evidence that keeping a coral reef aquarium at anything other than natural levels is preferable. It appears to be common practice to keep marine fish, and in many cases reef aquaria, at somewhat lower than natural salinity levels. This practice stems, at least in part, from the belief that fish are less stressed at reduced salinity. Substantial misunderstandings also arise among aquarists as to how specific gravity really relates to salinity
, especially considering temperature effects.
Ron Shimek has discussed salinity on natural reefs in a previous article
. His recommendation, and mine as well, is to maintain salinity at a natural level. If the organisms in the aquarium are from brackish environments with lower salinity, or from the Red Sea with higher salinity, selecting something other than 35 ppt may make good sense. Otherwise, I suggest targeting a salinity of 35 ppt (specific gravity = 1.0264; conductivity = 53 mS/cm)."