Pool Stains in Murphy, TX — Brown, Green, and Black Explained
That stain on your Murphy pool floor isn't just dirt. The color tells you exactly what caused it — and each one needs a different fix.
You brushed a dark spot on the pool floor and it didn't move. You hit it with a scrub brush — still there. You dumped chlorine directly on it and came back the next day — still there. Now you're worried it's permanent damage to the plaster, or that something is fundamentally wrong with the pool.
Pool stains frustrate Murphy homeowners because they resist the normal cleaning methods that work for everything else. A leaf stain doesn't respond to chlorine the way algae does. An iron stain doesn't brush off the way calcium scale does. And a black algae stain requires a completely different protocol than either one. The fix depends entirely on what caused the stain — and the color is your diagnostic tool.
For homeowners in Maxwell Creek, Mustang Park, and Murphy Heights, stains tend to follow predictable patterns tied to the neighborhood's tree canopy, soil composition, and pool age. Here's how to identify what you're looking at and treat it correctly.
The Color Diagnostic
Brown and Rust Stains — Metal (Iron or Manganese)
What it looks like: Reddish-brown, rust-colored, or dark brown spots or patches on the pool floor, walls, or steps. May be concentrated in areas with poor circulation (corners, behind ladders, near the main drain). Sometimes appears as a full-floor brown tinge rather than distinct spots.
What caused it: Dissolved iron in the water that was oxidized — either by chlorine or by contact with the air at the waterline. When free chlorine reacts with dissolved iron, the iron converts from its invisible dissolved form (ferrous) to its visible oxidized form (ferric), which deposits as rust-colored particles on pool surfaces.
Iron enters Murphy pools primarily through municipal fill water (trace levels that accumulate over time) and through soil contact — North Texas clay soil contains iron, and groundwater seeping through pool shell imperfections can introduce iron directly to the plaster surface.
The vitamin C test: Crush a vitamin C tablet (ascorbic acid) and hold it against the stain for 30 seconds. If the stain lightens significantly, it's iron. This test is fast, cheap, and definitive.
Treatment: For localized iron stains, apply crushed vitamin C directly to the stain with the pump off — let it sit for 5-10 minutes, then brush. For widespread iron staining, add 1 pound of ascorbic acid per 10,000 gallons to the entire pool. The stains should lift within 2-6 hours.
After ascorbic acid treatment, immediately add a metal sequestrant to bind the now-dissolved iron and prevent re-staining. Don't shock the pool for 48 hours after treatment — chlorine will re-oxidize the iron and create new stains.
Green and Teal Stains — Copper
What it looks like: Green, teal, or blue-green discoloration, often concentrated around returns, near the heater outlet, or on lighter-colored plaster areas. Can appear as a waterline ring or as spots where copper-laden water dripped or pooled.
What caused it: Dissolved copper that precipitated out of solution, typically when pH spiked above 7.8. Common sources in Murphy pools include copper heat exchangers in older pool heaters, copper-based algaecides, and occasionally copper plumbing segments in pre-2005 construction.
Distinguishing from algae: Copper stains and green algae look similar from a distance. The key difference: algae brushes off (at least partially) and has a slimy or fuzzy texture. Copper stains are smooth, don't brush off, and have a more metallic or uniform appearance. Algae also responds to chlorine — copper stains don't.
Treatment: Copper stains are harder to remove than iron. A citric acid treatment (1 pound per 10,000 gallons) can lighten copper staining. For stubborn deposits, a direct application of a citric acid paste (citric acid mixed with water to a thick consistency) held against the stain for several minutes may be needed.
For severe copper staining that doesn't respond to citric acid, professional acid washing of the plaster surface is the last resort. This is a more invasive process that removes a thin layer of plaster along with the stain.
Organic Stains — Leaves, Berries, Tannins
What it looks like: Brown, tan, or yellowish stains in the shape of a leaf, cluster of berries, or an irregular organic form. Usually on the pool floor in areas where debris sat undisturbed for an extended period.
What caused it: Leaves, berries, acorns, or other organic material that settled on the pool surface and wasn't removed within a few days. As the material decomposes, it releases tannins and other organic compounds that stain the plaster beneath it.
In Murphy, organic staining is most common in fall (October-November) when the maturing tree canopy in neighborhoods built in the early 2000s drops significant leaf volume, and in spring when pecan catkins and oak tassels accumulate. Murphy Heights and the neighborhoods along Murphy Road have enough tree cover to produce meaningful leaf litter that reaches pools.
The chlorine test: Place a trichlor tablet directly on the stain (with the pump off) and weight it down with a smooth stone. Leave it for 24 hours. If the stain lightens, it's organic. The concentrated chlorine bleaches the tannin stain.
Treatment: For light organic stains, a concentrated chlorine application (granular cal-hypo sprinkled directly on the stain with the pump off, left for 30-60 minutes) usually lifts them. For deeper stains, a full pool shock to 20+ ppm combined with brushing can remove organic discoloration over 24-48 hours.
Prevention: The simplest prevention is removing organic debris before it sits long enough to stain — daily skimming during fall and spring pollen season. A robotic pool cleaner running daily picks up settled debris that the skimmer misses. If leaves accumulate for more than 2-3 days on the plaster, staining risk increases significantly.
Black Spots — Black Algae
What it looks like: Small (dime to quarter-sized) dark black or very dark green spots that are slightly raised and feel rough or gritty to the touch. Often appear on vertical surfaces (walls), in corners, and around fittings. May appear in clusters.
What caused it: Black algae (actually a cyanobacterium) that has rooted into the plaster surface. Unlike green algae that floats or forms a surface film, black algae sends roots into porous surfaces — plaster, concrete, and grout — and produces a protective waxy layer on top that shields it from chlorine.
This is the most difficult pool stain to treat because it's not technically a stain — it's a living organism embedded in your pool surface. Standard chlorine levels and normal shocking don't penetrate the protective layer.
Treatment protocol:
- Brush aggressively with a stainless steel algae brush (not nylon — nylon is too soft to break the protective layer). Brush each black spot directly, pressing hard enough to crack the waxy coating.
- Immediately after brushing, press a trichlor tablet directly against each brushed spot and hold it for 30-60 seconds. The concentrated chlorine penetrates the cracked protective layer and kills the organism beneath.
- Shock the entire pool to 30+ ppm (triple shock dose). This is an extreme chlorine level, but it's what the protective layer requires for reliable kill.
- Brush again 12 hours later and maintain elevated chlorine for 72 hours.
- Test and retest. Black algae returns if even a small amount survives. Monitor the treated spots for 2-4 weeks. If any reappear, repeat the treatment on those specific spots.
Why black algae is uncommon but serious in Murphy: Murphy's pool stock is reaching the 15-20 year age range in some neighborhoods. Older plaster becomes more porous with age, giving black algae more surface area to root into. Pools with deteriorating plaster, unmaintained grout lines, or rough spots from previous acid washing are most vulnerable.
The Right Order: Identify Before You Treat
The single biggest mistake with pool stains is treating without identifying. A homeowner who assumes a brown stain is organic (and shocks the pool to treat it) may actually be oxidizing dissolved iron — making the iron stain worse and more widespread.
Before treating any stain:
- Identify the color. Brown/rust = metals. Green/teal = copper. Brown organic shapes = leaves/tannins. Black raised spots = black algae.
- Test with vitamin C and chlorine. Vitamin C lightens metal stains. Chlorine lightens organic stains. If neither works, it's likely copper or black algae.
- Test your water for metals. If iron or copper levels are elevated, address the metal contamination first, then treat the stains. Treating stains without addressing the source means they'll return.
- Then treat with the appropriate protocol for the identified stain type.
Stain Prevention for Murphy Pools
A few habits specific to Murphy's conditions that minimize staining:
Skim daily during fall leaf season. Murphy's maturing neighborhoods produce increasing leaf litter each year. What was a minor issue five years ago becomes a significant organic staining source as trees grow.
Maintain pH at 7.2-7.4. Higher pH accelerates both metal precipitation (creating metal stains) and calcium scaling. Lower pH keeps metals in solution where they can be managed with sequestrants rather than depositing on surfaces.
Use a metal sequestrant if you have detectable iron or copper. A monthly maintenance dose prevents gradual accumulation from reaching the threshold where staining occurs.
Don't let the pool sit without chlorine. Even a few days of zero chlorine — during a pump failure, power outage, or vacation — can allow organic contaminants to stain surfaces that would normally be oxidized and kept clean by active chlorine.
Stains you can't identify or remove? Hydra Pool Services diagnoses pool stains and applies the right treatment — no guesswork — across Murphy, Frisco, Plano, McKinney, Allen, Parker, and The Colony. Book a pool assessment →