Green stuff on the court: algae, mold and tannin stains

The green on a shaded court is not dirt and it does not wash off in the rain. It is algae, with mildew for company in the damp corners, and if the court is under oaks or maples it has leaf stains to go with it. All three are a drainage and shade problem wearing a biology costume. Here is what each is, how to clean it without taking the surface off with it, and the only fix that keeps it from coming back.

Algae

Algae needs water and shade, and a court gives it both at the low end, along the north fence, under the trees, and in every birdbath. It shows as a green film that is slick when wet, which is the real problem: a player's foot on wet algae goes out from under them. It also holds moisture against the acrylic, which softens it, and traps grit, which grinds it. A court with algae wears out faster at exactly the places that were already the wettest.

Mildew and mold

Black or gray spotting in the same places, usually in the texture of the surface rather than on it. Same cause, same fix, a little harder to shift because it has roots in the sand.

Leaf and seed stains

A wet leaf left on a court for a week leaves a brown shadow of itself: tannins leach out and dye the acrylic. Oak leaves and the helicopter seeds from maples are the worst; so are the berries that birds drop from the fence line. The stains are permanent in the sense that they are in the color, not on it. Most fade over a season of sun; the dark ones are there until the next resurfacing.

Cleaning that works

1. Sweep or blow the court clean, including the fence line and the corners where leaves pile.
2. Mix a cleaner: a cup of household bleach, or an oxygen-based cleaner, in a gallon of water, with a squirt of dish soap to help it wet the surface. Keep it off the lawn.
3. Wet the green areas with the mix and leave it for ten or fifteen minutes. Do not let it dry.
4. Scrub with a soft-bristle push broom; the algae lets go once it is dead.
5. Rinse with a hose, or a pressure washer with a wide fan tip at no more than 1,500 psi, the wand kept moving and held a foot or more off the surface, until the water runs clear. Never a zero-degree nozzle, never a turbo tip, never held still: that is how a well-meaning volunteer puts a bare stripe into a court that lasts until the next resurfacing.

Twice a season on a shaded court, once on a sunny one. It takes a morning for a court and it is work a club can do itself.

Cleaning that damages

Pressure washers set high and close, which strip the color. Muriatic acid, which eats the acrylic. Wire brushes. Leaving bleach to dry on the surface, which leaves a pale patch. Any cleaner with a solvent in it. If in doubt, soap, bleach and a broom.

The fix that lasts

Algae grows where water sits, so the cure is drainage and light. Level the birdbaths. Clear the drains and the swale along the high side so the lawn's water goes around the court, not across it. Trim or remove the trees that shade the court from the south and drop leaves on it; a court in full sun almost never has algae. Blow the leaves off in November before they lie wet for the winter. And when the court is resurfaced, ask for a lighter color on the surround, which dries faster and shows the green sooner so it gets cleaned.

On the site walk we note where the algae is, because it is a map of where the water goes. The puddles article covers the leveling; the maintenance calendar has the washing months.