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Hey there, fellow pool owner! As a nature photographer, I've seen my share of interesting growth patterns, and those black spots sound like they could be organic. Have you checked if they're algae or maybe even mold? Before you panic, try gently brushing a small area with a soft brush—if it comes off easily, it's probably organic growth. Sometimes shocking can temporarily make existing issues more visible as it reacts. What's your water chemistry looking like with that Leslie's kit? pH and alkalinity in balance?

FloatFreak might be onto something with the organic angle, but let me approach this from a biohacker perspective. Black spots after shocking could indicate a mineral imbalance or oxidation reaction. Have you tested for metals like copper or iron in your water? Chlorine shock can oxidize dissolved metals, causing them to precipitate and stain plaster. Also, what type of shock did you use? Calcium hypochlorite? If so, and if your water is hard, you might be dealing with calcium scaling that's trapping contaminants. Run a metal test and consider a sequestrant if metals are high.

Tech gadget lover here—first, don't panic! Data is key. What specific readings are you getting from your Leslie's test kit? Break down the numbers: free chlorine, total chlorine, pH, alkalinity, calcium hardness, and cyanuric acid. Black spots spreading suggests an ongoing reaction. Could be black algae, which has deep roots and needs aggressive brushing and sustained high chlorine. Or, as DiveMaster said, metal staining. I'd recommend documenting with photos to track spread rate. Also, consider a stain test: rub a vitamin C tablet on a spot (if it lightens, it's iron) or hold a trichlor tablet on it (if it lightens, it's organic).

Great points, everyone! To add a natural observation: in my photography, I've noticed that environmental stressors (like sudden chemical changes) can make underlying issues 'bloom.' If it's black algae, it's tough but treatable—you'll need to brush thoroughly to break the protective layer, then maintain elevated chlorine levels for days. But if it's staining from metals, that's a different protocol. NoodleNinja41's stain test idea is smart! Also, what's your water source in Nevada? Well water often has metals. Keep us posted with those test results and maybe a photo if you can!

Building on the biohacking angle: if metals are the culprit, it's about chelation. A sequestrant (like HEDP or phosphonic acid-based products) can bind metals to prevent staining. But caution—if you overdose, it can cloud the water. Also, check your shock's purity; some cheaper shocks have fillers that contribute to issues. For a holistic approach, balance all parameters first: pH 7.4-7.6, alkalinity 80-120 ppm, calcium hardness 200-400 ppm. Then address the spots. And remember, shocking in hot Nevada sun can degrade chlorine fast—did you shock at dusk for better efficacy?

Exactly! Systematically: 1) Test and log all chemistry. 2) Perform stain tests (vitamin C for iron, trichlor for organic). 3) If organic, brush aggressively and maintain FC at shock level for your CYA (use the [Chlorine/CYA Chart](https://www.troublefreepool.com/calc.html)). 4) If metals, use a sequestrant and avoid high pH. 5) Monitor with photos. Wrong treatment? Possibly if you shocked without balancing other params first, or if the shock type was wrong for your water. But don't stress—this is fixable! Tech tip: there are pool apps to track chemistry trends; might help prevent future issues.