Nothing takes the fun out of a backyard swim faster than looking down and seeing streaks and splotches creeping across your pool walls. The good news? Those stains aren't permanent, and you don't need a chemistry degree to deal with them. Once you know what caused a stain, removing it and keeping it from coming back is surprisingly straightforward. Here's everything a Twin Cities pool owner needs to know.
Step 1: Figure Out What Caused the Stain
Pool stains almost always trace back to one of two sources: organic matter or metal. Nailing down which one you're dealing with matters, because the fix is completely different for each. Leaves and yard debris tend to be the culprit for uncovered pools (an automatic pool cover goes a long way here), while metal staining is common in pools fed by well water or plumbed with copper or aging metal equipment.
Not sure which you've got? The color of the stain is your best first clue:
- Green, brown, or red: Points to iron in the water, which is typical of well-fed pools or pools with nearby iron sources like a metal fence.
- Bright red or blue: Usually berries from nearby shrubs or trees.
- Brown to black: Often manganese, which shows up in plenty of municipal water supplies.
- Green and brown together: Almost always plant matter that's been resting against the wall for a while.
- Green, black, or blue: Typically organic debris like sticks and leaves. If there's little greenery near your pool, suspect corroded copper plumbing instead.
Step 2: Confirm It With a Quick Stain Test
Color gives you a strong hunch; a simple test confirms it before you commit to a treatment.
- Testing for metal: Hold a bit of chlorine against the stain. If nothing happens, metal is likely. Follow up with a pinch of ascorbic acid (vitamin C) powder. If the stain lightens or lifts, you've confirmed metal.
- Testing for organic: Apply a small amount of chlorine directly to the spot. An organic stain will lift easily.
Step 3: Remove the Stain
With the source confirmed, it's time to clear it out.
- Organic stains: Chlorine is your friend. Because your water already has some, you'll want to hyper-chlorinate with a calcium hypochlorite shock. Do this at dusk so the chlorine has time to work overnight without burning off in the sun.
- Metal stains: Reach for a stain remover formulated for the specific metal behind the problem. If you're not certain which metal you're fighting, check with a maintenance specialist before treating so you don't waste product on the wrong fix. Keeping your pool chemicals stocked and balanced makes this far easier.
When staining is severe and treatments aren't cutting it, it may be time to acid wash and resurface the pool. Our acid washing service can bring a badly stained surface back to life.
Step 4: Keep Stains From Coming Back
Prevention isn't complicated. It just takes a little consistency:
- Keep your water properly balanced and sanitized at all times. Our guide on proper pH and chemical ratios is a great starting point.
- Vacuum weekly or run a robotic cleaner so debris never settles on the surface.
- Skim organic matter off the water as soon as you spot it.
- If fruit-bearing trees or bushes hang near the pool, consider relocating them out of drop range.
- Inspect for stains weekly. Catching one early is the easiest stain you'll ever remove.
Want the fundamentals in one place? Our overview of basic pool maintenance every owner should know pairs perfectly with this guide. And if DIY upkeep isn't your thing, a standing weekly or bi-weekly service schedule keeps staining from ever getting ahead of you and saves you from resurfacing more often than you should have to.
Let Royal Pool & Spa Keep Your Water Crystal Clear
Tired of scrubbing stains and second-guessing your chemicals? Let us handle it. Royal Pool & Spa has served White Bear Lake and the greater Minneapolis–St. Paul area since 1988, and every one of our pool techs brings at least 10 years of hands-on experience. Whether you're across the Twin Cities metro or right around the lake, we'll build a weekly or bi-weekly maintenance plan that keeps your pool looking its best all season.
Call us today at 651-779-7606 or send us a message and we'll be in touch. Curious what sets us apart? See our difference.