|Moisture. Always make sure the container is well sealed as soon as you are finished with it. Do not store the salt measuring cup in the salt container as it often collects moisture while being used. Bags of salt are best stored inside a plastic container with a good seal.
Aquatic Technician Tip: When mixing saltwater for marine aquariums, always fill your container with all the water you will need BEFORE adding the salt. A salt overdose can cause the calcium to precipitate out, lowering pH to dangerous levels.