It is extremely important to keep your reef at a proper salinity level. Any drastic change in salinity will affect you corals in a negative way. Many simple reef organisms are unable to regulate their internal ionic balance of sodium chloride and other elements found in natural seawater. These organisms are often known as osmoconformers. Osmoconformers are marine invertebrates that maintain their internal salinity such that it is always equal to the surrounding seawater. They also keep their body fluids isotonic to the external environment by actively regulating their internal concentration of amino acids, ions, and proteins to match the osmolarity of the environment. Basically when you change the salinity or drastically alter the chemistry of your water numerous organisms must adapt its internal chemistry. Some of these organisms will spend up to 80% of their metabolic energy maintaining their internal cellular balances. As we know providing nutrients to our organisms can be a challenge and to make them work harder to survive simply because we allow fluctuating salinity levels only add insult to injury and only creates undo stress on many important simple reef organisms.
We recommend a salinity of 34 to 35 ppt salinity or 1.024 to 1.026 specific gravity depending on average temperature. Natural sea water ranges from 30 to 40 ppt salinity. The 30 being lagoons after a heavy rain fall to 40 ppt salinity in the read sea. Most of the ocean is between 35 and 36 ppt salinity. It is important to note that fresh water is less dense than salt water and organisms subject to varying salinity due to heavy rainfall are generally adapted to the lagoon and are found in the upper portions of the reef. Temperature can affect your salinity as well. At 78 degrees Fahrenheit a salinity of 34.1 ppt is 34.9 at 82 degrees Fahrenheit. This is why we recommend keeping things constant.
We highly encourage you to maintain the salinity of your systems at normal reef conditions between 35 and 36 ppt salinity. All reef inhabitants will suffer damage from prolonged exposure to lowered salinity. Invertebrates kept at low salinity often die within a few days to a few months. Given that corals, sea anemones, sponges and some other invertebrates do not age or can be considered immortal, low salinity result in their quick and untimely death. Such a shame as it is easy to keep salinity constant. Some mollusks, crustaceans and most fish kept at low salinity will eventually die of kidney failure. A fish that dies in a couple of years in an aquarium could have lived over 20 years had the salinity been appropriate. For treating Ich with hypo salinity click here.