The Pool Isn’t Green Because It’s Hot

**What if your green pool isn’t really a “green pool problem” at all?** This week on **Pool Envy**, we go way past the usual *“it’s hot, add more chlorine”* advice and into what’s actually happening inside the water. Why can algae show up even when the pool tests like it has chlorine? What role does CYA really play? Why can poor circulation create opportunities for growth? And why does killing algae not necessarily mean you’ve removed what fed it? To make sense of it, we’re taking an unexpected detour into a **strange 1970s liminal-space warehouse filled with waterbed mattresses, buzzing fluorescent tubes, leaking containers, and one very questionable quarter-operated machine**. Somehow, by the time we leave, phosphates, sequestration, oxidation, circulation, filtration, microbial growth, and nutrient recycling all make a lot more sense. We’ll also talk about why swimming-pool water is not sterile, why microbes are inevitable, how the sourdough-starter analogy explains algae better than most chemistry lectures, why **“I have chlorine”** may be the beginning of the conversation instead of the end, and why an old filter can become far more involved in the biology of a pool than most homeowners realize. Copper? Phosphates? Dead algae? CYA? Biofilm? Old filter media? Yep. And through all of it, one idea keeps coming back: **Contained isn’t removed.** **Dead isn’t gone.** **And algae doesn’t need an invitation — it needs an opportunity.** If you’ve ever looked at a pool that went green seemingly overnight and thought, **“How the hell did that happen?”** — this episode is for you. You may never look at your pool water the same way again.  Sometimes the reflection is the least interesting thing happening in the pool.