Algae Water Feature in Charleston

Algae Water Feature — practical Lowcountry troubleshooting: what to verify first, safe next steps, and when the fix needs a licensed pro.

Algae in a recirculating water feature is almost always a circulation, organics, or light problem first — and a “chemicals” problem second. In Charleston’s long warm season, small imbalances turn green fast. The goal is to fix what feeds the algae, not only what color the water is today.

Field note: String algae, green water (phytoplankton), and a slippery film on rockwork are different conditions; they share some fixes (more movement, less debris, less sun on still zones) but not identical treatment paths.

What you are probably seeing

Green water — the basin looks like pea soup; you can’t see the bottom. String / hair algae — clumps on stone or in the streambed. Film or matte coating on spill stones — often organics + biofilm, not “just” minerals. Rebound after a heavy rain or pollen week is common: oak debris and roof runoff add nutrients in a day.

Why it happens here (Charleston-specific)

Heat and long sun hours extend the growing season for algae. Live oak and pine debris, plus lawn and bed fertilizer drift, add nitrogen and phosphorous to the system. If part of the feature is shaded and part is in full sun, you can have still, warm, nutrient-rich water in one zone while the pump and spillway look fine at a glance. Coastal properties may also see faster hardware fatigue — clogged intakes and weaker flow read as “algae” from the owner’s perspective.

Diagnosis checklist (before you spend)

• Confirm run time and flow — is the pump running on the schedule you think it is, and is flow visibly full at the weir / spill? Weak flow creates slack-water algae beds.
• Skim and bag debris — screen intakes, biofalls, and reservoir grates; one clogged intake mimics a “chemical” failure.
• Check sun + plant debris — a spill stone that never dries will favor film algae; a sunny pond edge with muck on the bottom favors green water.
• Water chemistry (where applicable) — pH and alkalinity affect how algaecides and beneficial bacteria behave; if you’re already treating, verify tests are from a moving sample, not a stagnant corner.

Remediation paths (high level)

Most durable outcomes increase turnover, remove organics, and only then target algae. Options might include re-leveling weirs for even flow, re-seating boulders that created still pockets, adjusting plantings that dump debris into the stream, or upgrading / servicing pumps and lights (UV, where specified) as part of the plan — not as a stand-alone “spray and pray” pass.

When to bring in a contractor

Stop at DIY for anything involving electrical, gas, or structural work on the feature. If the basin has to be drawn down for an intake repair, if liner or plumbing is suspected, or if grading sends stormwater and lawn runoff into the reservoir, you need a scoped fix — not another bottle of algaecide. DCM Outdoor documents hydraulics, access, and inspection points so the same algae problem is not re-bid next season.