Gloeocapsa Magma
Gloeocapsa magma is a photosynthetic cyanobacteria that feeds on the limestone calcium carbonate filler embedded in asphalt shingles. It is the organism responsible for the black or dark-gray streaks that run from ridge to eave on millions of American roofs. Algae spores are carried by wind, birds, and squirrels, which is why you'll often see streaks appearing on one slope of a roof before the other, and why entire neighborhoods in Madison begin showing streaks within a few years of each other once the spore population establishes locally.
In depth
Left untreated, Gloeocapsa shortens shingle life by consuming the limestone filler and weakening the mat structure, and it voids some manufacturer warranties if the infestation is documented in a home inspection. The ARMA-recommended treatment is a low-dwell (10-minute minimum) soft wash with sodium hypochlorite at 1-2% concentration at the shingle surface, which kills the organism at the root. Results show progressively over 2-8 weeks as rain rinses the dead biomass off.
How this shows up on our jobs
Gloeocapsa magma is the reason for black-streaked shingles across Madison's residential neighborhoods. We kill it with soft wash and install zinc strips to prevent regrowth for a decade.
Services where this matters
Related terms
Moss vs. Lichen
Moss and lichen are both organisms that colonize roofs and exterior surfaces in Wisconsin, but they are biologically distinct and require different removal strategies. Moss is a non-vascular plant that holds moisture against the surface — on a shingle roof, trapped moisture under a moss mat accelerates granule loss, lifts shingles, and leads to freeze-thaw damage at the mat's edges. Moss is soft, green, and responds well to sodium hypochlorite soft washing plus a zinc-strip regrowth inhibitor.
Algae vs. Lichen
Algae (most commonly Gloeocapsa magma on roofs) is the photosynthetic organism responsible for the black streaks running down asphalt shingles, the green haze on north-facing siding, and the slippery film on concrete walkways. Lichen is a symbiotic partnership between a fungus and an alga — a completely different, far more persistent organism that looks like a flat crusty patch with a raised perimeter. Lichens physically anchor into the substrate with root-like structures, which is why they do not wash off like algae does.
Soft Wash
Soft washing is a low-pressure exterior cleaning method that uses biodegradable detergents and a controlled bleach solution to kill the algae, mold, mildew, and bacteria that cause staining — rather than scouring them off with brute force. A soft wash rig delivers cleaning fluid at roughly 60-200 PSI, comparable to a strong garden hose, which is safe on siding, shingles, painted surfaces, screens, and caulking. The chemistry does the work: the solution dwells on the surface, breaks down the organic growth at the cell level, and is then rinsed clean with fresh water.
Sodium Hypochlorite
Sodium hypochlorite (NaOCl) is the active ingredient in household bleach and the primary disinfectant used in professional soft washing. It is sold to exterior cleaners in 12.5% concentration (commonly called "SH" or "pool shock"), roughly twice the strength of consumer bleach. When applied in a properly mixed soft-wash solution, it kills algae, mold, mildew, lichen, and bacteria at the cellular level within minutes and breaks down into salt water and oxygen.
Biocide
A biocide is any chemical agent that kills living organisms — bacteria, fungi, algae, mold, mildew, lichen. In exterior cleaning, the most common biocides are sodium hypochlorite (bleach), quaternary ammonium compounds ("quats"), and hydrogen peroxide. Each has a place: sodium hypochlorite is the fastest and most cost-effective broad-spectrum kill; quats provide residual antimicrobial action that slows regrowth on treated surfaces; peroxide is the mildest and is used where chlorine would damage the substrate.