When should you reorder salt ?
Lift the lid of your tank. Two signs are enough: if the level has dropped below halfway, or if you can see water above the salt, the time has come.
An empty tank for a few days damages nothing, but the water turns hard again immediately and scaling picks up where it left off. The common mistake is waiting until you can see the bottom: by then, regeneration has already been incomplete several times over. Get into the habit of looking once a month; it takes ten seconds.