---
title: "Biocides in Exterior Cleaning: How Pros Kill Algae and…"
description: "Definition of Biocide: what it means in pressure washing and exterior cleaning, how it applies to Madison, WI home and commercial cleaning services."
url: https://www.thetotalwash.com/glossary/biocide
source: https://www.thetotalwash.com/glossary/biocide
generated: 2026-06-13T03:59:58.230Z
---

Chemicals & Detergents

# 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.

## In depth

In regulated settings (food-service exteriors, healthcare facilities, certain municipal contracts) biocide use is governed by EPA registration, label rate, and state pesticide-applicator rules. A professional tracks kill concentration at the surface (not in the bucket), documents dwell time, and matches biocide choice to the target organism. On a residential roof, that means getting 1-2% sodium hypochlorite at the shingle for at least 10 minutes of dwell — what the industry now considers the ARMA-endorsed baseline for effective algae kill.

## How this shows up on our jobs

Every soft wash we perform is a biocide application. We document chlorine concentration, dwell time, and landscape pre-soak on commercial jobs for compliance and warranty purposes.

### Services where this matters

[Roof Cleaning](/residential/exterior-cleaning)[House Washing](/residential/exterior-cleaning)

## Related terms

[Sodium HypochloriteSodium 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.](/glossary/sodium-hypochlorite)[Soft WashSoft 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.](/glossary/soft-wash)[Dwell TimeDwell time is the interval between applying a cleaning chemistry to a surface and rinsing it off. It is the single most misunderstood variable in exterior cleaning. Chemistry does not clean instantly; it needs time to break chemical bonds, kill organisms, or dissolve minerals. Too little dwell and the chemistry is wasted. Too much dwell — especially in direct sun — and the chemistry can damage the surface, bleach landscaping, or drive the stain deeper.](/glossary/dwell-time)[Mildew vs. MoldMildew and mold are both fungi, but they behave differently. Mildew is a flat, surface-level growth — usually white, gray, or yellowish — that stays on top of a substrate and can typically be cleaned away with soft-wash chemistry. Mold is three-dimensional and penetrates into porous materials (wood, drywall, paper), spreading its hyphae deep into the structure. On exterior surfaces, what most homeowners call "mold" is often mildew or algae; true structural mold on the outside of a house is uncommon without an underlying moisture problem.](/glossary/mildew-vs-mold)[Algae vs. LichenAlgae (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.](/glossary/algae-vs-lichen)

## Need this service in Madison?

The Total Wash Co. handles biocide and every other exterior cleaning service in the greater Madison, WI area. Get a free, no-obligation quote.

[Get a Free Quote](/instant-quote)[Call (608) 360-5818](tel:+16083605818)

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