Zero chlorine is one of those pool problems that feels impossible because you can do everything “right” and still watch your sanitizer disappear. We dig into the real reasons it happens, especially after adding stain removers and sequestering agents meant to solve metal stains and protect surfaces. 

From there, we get clear about metal chemistry and a common misconception in pool maintenance: a sequestering agent doesn’t remove metals from pool water. It temporarily binds them, then sunlight and oxidizers break that binder down and the metal can stain again. We explore why product selection matters, how overdosing makes the problem worse, and why some treatments can raise phosphate levels that algae love. If you’re trying to protect new plaster or avoid dropping metals out of solution, this is where water care becomes a careful balancing act.

We also unpack a major source of “mystery” chlorine loss: sodium bromide based algae products. Add bromide and you can effectively turn a chlorine pool into a bromine pool, where every chlorine dose reactivates bromine instead of building a chlorine residual. That creates confusing test results, higher sanitizer targets, and fast sunlight burn-off because cyanuric acid doesn’t protect bromine the same way. We close with the non-negotiable safety message: a pool with zero sanitizer residual has no protection against waterborne infection risks, and “negative demand” can hide how much chlorine the water is actually consuming.

• stain removers and some sequestrants creating immediate chlorine demand
• overdosing metal treatment chemicals making chlorine loss worse
• phosphonate and phosphate breakdown raising algae risk
• why sequestering agents do not remove metals from water
• metal removal as an alternative to ongoing sequestration
• sodium bromide products converting chlorine pools to bromine pools
• test kit confusion when bromine reads like chlorine
• sunlight destroying bromine faster without cyanuric acid protection
• zero chlorine safety risks including infection transmission
• negative chlor

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