Generally there are two main types of corals - hard and soft. The framework of a coral reef is composed of the calcareous skeletons of many corals. As a coral grows new polyps replace old polyps which become the calcareous skeleton. Humans need food, water and shelter to survive. So the marine enviroment is very important to them,especially the nutrition of the aquarium enviroment. Blue Treasure Synthetic Sea Salt made by according to natural marine enviroment. Blue Treasure Synthetic Sea Salt could make the nutrition element achieve level Mg-1350mg/L, Ca-420mg/L, kH-9'C dH, Sr-9.5mg/L. Why we make the level a little higher than natural sea water, because people keep corals in a closed type enviroment and lack circulation of natural sea water, so during breeding coral reef, they will consume more nutrition. Coral reef need more supplement nutrition for growth.