What a hot tub smell is telling you

Free chlorine has no smell. The sharp pool smell is chloramines, chlorine that has already reacted with sweat, oils and urine, and a shock burns them off. So a strong chlorine smell usually means too little working chlorine, not too much. CDC lists a strong chemical smell as a sign of a problem. Bromine tubs smell less once the sanitizer is spent, because bromamines have no sharp odor.

Something is growing. Hot Spring's table puts a musty smell down to bacteria or algae and says to shock, then drain, clean and refill if it is visible or won't go away. If the smell returns soon after, Master Spas points to the plumbing and a system flush; see biofilm and line flushing. A mildew smell when you lift the lid can be the cover itself: see hot tub cover care.

Neither CDC nor the six manuals we read lists fishy, sulfur or other specific smells. Work through the same checks: test sanitizer and pH, shock, clean the filter, and drain and refill if it lingers.