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**As a skeptical mom who researches everything**, I'd say start with the simplest explanation first! Those black/green spots are *probably* algae, especially if you're in humid Ohio. Have you tested your chlorine levels? Algae thrives when sanitizer is low. Try brushing a spot—if it's slimy or comes off easily, it's algae. Metal stains (from iron or copper) tend to be more stubborn and might not brush off. Also, check if you've been using well water or algaecides with copper, which can cause staining. But honestly, algae is way more common—don't overcomplicate it!

**Tech gadget lover here**—I'd approach this with data! Get a pool water test kit that measures metals (iron/copper) *and* sanitizer levels. Some digital testers even connect to apps. If metals are high (>0.2 ppm), stains are likely. Also, algae often shows up as green fuzzy patches, while metal stains can be darker black/brown and more spread out. Have you tried a vitamin C tablet test? Rub it on a spot—if it lightens, it's iron. Or use a chlorine tablet—if it bleaches, it's algae. Tech doesn't lie!

**Marathon runner perspective**—consistency matters! In my experience, algae blooms happen when pool maintenance slips (like after a vacation or heavy rain). Ohio's summer heat and humidity are perfect for algae. Are the spots in shaded areas? Algae loves low circulation spots. Metal stains might be more uniform. Quick fix: shock the pool and brush. If spots disappear after 24-48 hours, it was algae. If not, consider a metal sequestrant. But honestly, 90% of the time in fiberglass pools, it's algae—just stay on top of your chemical balance!

**CrossFit junkie here**—go aggressive! Black spots could be black algae, which is nasty and roots into surfaces. It doesn't brush off easily and needs heavy scrubbing with a stainless steel brush (safe for fiberglass). Green is usually regular algae. Metal stains? Less common unless you have old pipes or fill with well water. Try this WOD: 1) Test water, 2) Shock pool, 3) Scrub spots, 4) Re-test. If no change, hit it with ascorbic acid (vitamin C) for metals. But fiberglass is non-porous, so algae is the usual suspect—don't let it win!