Clean Freaks Co. Paver cleaning in Jupiter Island.

On a narrow Atlantic barrier island, a paver terrace, pool deck, or motor court lives inside a marine climate that never fully dries out. Salt aerosol carried off the surf settles into the surface texture and the joint sand, humidity keeps the stone damp long after rain, and the dense canopy of sea grape and palm holds shade over large sections of the field. That combination is exactly what black algae — the dark, crust-like staining most owners mistake for dirt — needs to colonize porous paver faces, and it is why a barrier-island field greys and darkens far faster than the same pavers set inland.

The materials complicate the work further. Coquina and shell-stone are naturally porous and mineral-soft; they hold salt and organic growth deep in the pore and cannot take the tip pressure a hard clay or concrete paver tolerates. Push too hard and you etch the shell matrix, blow out the polymeric sand between units, and open joints that then trap more sand and salt. The correct treatment is chemistry-led and low-pressure — a dwell that kills the organic growth and flushes chloride from the pore — not a high-pressure pass that only strips the surface and leaves the root behind.

Efflorescence is the third variable. Salt and mineral drawn up through damp pavers dries as a white bloom on the face, and it reads nothing like algae; treating one as the other wastes a visit. Reading coquina, salt bloom, and shade growth apart before a drop of chemistry is applied is what separates a partner who understands this island from a crew with a pressure hose.

1. Identify the paver — coquina, shell-stone, clay, or concrete — and test an inconspicuous joint, because mineral-soft shell and salt-loaded joint sand set the pressure ceiling and rule out any tip that would etch the face or evacuate the polymeric sand.
2. Soft-wash the field with a sodium-hypochlorite or oxygen-based solution dosed to kill black algae and mildew at the root, held at dwell so the organic growth is lifted rather than merely knocked back and regrown by the next humid week.
3. Flush salt and chloride from the pore with generous low-pressure rinsing, then read the surface for efflorescence bloom and treat that mineral separately rather than mistaking it for remaining stain.
4. Re-sand and re-stabilize open joints with fresh polymeric sand where the growth or flushing has emptied them, so wind-driven island sand and salt cannot re-seat and re-seed the field between visits.

• Late spring, before hurricane season opens June 1 — clear the winter’s algae and salt load so storm debris lands on a sound, sealed field rather than an already-fouled one.
• Within days of a named storm or tropical system passing — salt-water flooding, palm shed, and organic wrack drive fast staining and joint washout that are far easier to reverse before they set.
• After the peak of the season, October into November — reset the field once the tropics quiet, flushing accumulated chloride and re-sanding joints opened by wind and surge.
• Following a winter nor’easter or king-tide event — heavier salt spray off a rough Atlantic settles into shell-stone pore and shows as film and bloom that want a dedicated flush.
• Ahead of a season opening or gathering, when a shaded, north-facing terrace has greyed under the canopy and needs the algae taken back to the pore.