For aquarists who depend on hydrometers for measuring their aquarium water's salinity, adequate salinity for their organisms is represented by specific gravity values in the range of 1.025 to 1.026. In spite of this, some manufacturers still recommend mixing artificial sea water to a specific gravity of about 1.022. Such a value results in salinities between 28 and 30 ppt, well outside the range for long-term survival of most coral reef organisms.
Coral reef animals are, indeed, delicate and hard to keep alive. Anybody can prove this by getting some of these animals and keeping them at temperatures that are abnormally low, abnormally high, or under salinity conditions that stress the animals to their maximum limits. Under such conditions, is it any surprise that the animals die when the slightest other factor goes wrong? It should not be, and neither should the observation that many of these animals also will simply just die from prolonged exposure to those conditions.