Get yourself a 1/2 cup scoop dedicated to mixing salt. The general rule of thumb is 1/2 cup salt to each gallon of water. Make sure you are using RODI
water, not tap, or you will find yourself fighting nuisance algae constantly. I also recommend a small heater and a powerhead to assist with the mixing and making sure you're not dumping cold water on your animals. Let it mix for several hours (24 hours is the general recommendation) to make sure it is thoroughly mixed. Be sure to check specific gravity (salinity) before adding new water. A refractometer is best, but many folks get away with hydrometers for years.