Sulphur/Sulphate
Sulphur is a macro element which is abundantly present in all reefs around the world mostly in the form of Sulphate.
Despite Sulphur being a macro element that typically gets replenished with water changes and the addition of foods or other supplements containing high levels of sulphate, sulphur can still get depleted in the tank. Given that Sulphur is highly linked to bacterial activity, the presence of Sulphur in much lower or higher concentrations from the normally found in the seawater can lead to bacterial issues.