Saltwater ich (ick), or "white spot disease" is one of the most common diseases that infect marine fish in home aquariums. It is caused by Cryptocaryon irritans, and is similar to freshwater ich. 

Many commercial Ich treatments utilize copper to kill the Ich parasite. This is fine in fish only aquariums, but copper is toxic to aquatic invertebrates like snails, crabs, shrimp and crayfish. 

The most common parasite in both fresh and saltwater is Ich (Ichthyophthirius multifiliis) or white spot. Others frequently found include Anchor Worms, Black Spot, Costia, Gil Flukes, Hexamita, Fish Lice… 

…of even one degree Farenheit in a day can cause enough stress on a fish to allow diseases such as ich to become a problem. It is important to control temperature as accurately as possible with both a heater…