Every April we get the same call: "It was fine last week." It was. Then three things happened at once, and a pool that coasted through winter on a tablet a week went green in about ten days.
The calendar
Late February to March: pollen
Pensacola's pine pollen is a yellow film on every car, and on every pool. It's organic matter, and organic matter eats chlorine. A pool that held a good residual all winter suddenly reads zero, and nobody changed anything.
March to April: oak tassels
The live oaks drop their tassels right behind the pollen. They sink, they collect in corners and on steps, and they're food for algae. In East Hill, North Hill and Cordova Park this is the heaviest debris month of the year.
The first 90-degree week
Warm water grows algae faster, and sunlight burns off chlorine faster. If the stabilizer level is low, which it often is after a rainy winter, a full chlorine dose can be gone by the next afternoon.
Add an afternoon storm
Rain dilutes everything and drops pH. Now the chlorine that's left is working less efficiently in water that's warmer than it's been since October.
Why the tablet stopped working
A chlorine tablet in a floater was enough in January because nothing was consuming chlorine. In April the demand is five times higher and the tablet dissolves at the same rate. The gap between what the pool needs and what it's getting is where the green comes from. It isn't a mystery product problem; it's arithmetic.
How to stay ahead of it
- Test twice a week from March on. Free chlorine and pH at minimum. If free chlorine reads under 1 ppm, the pool is already losing.
- Brush the walls. Algae starts as a slick film you can't see. Brushing weekly breaks it up so the chlorine can reach it.
- Empty the baskets. A full skimmer basket cuts circulation, and stagnant corners go green first.
- Check stabilizer once in spring. Cyanuric acid at 30 to 50 ppm keeps chlorine from burning off by noon. Below that, you're pouring chlorine into sunlight.
- Run the pump longer. Eight to ten hours a day in season. Circulation is half of chemistry.
If it's already green
Don't buy the bottle labeled "green to clean" and hope. Balance pH first, shock hard, brush, run the filter continuously and clean it as it loads, then vacuum the fallout. It's a several-day process. If that's more than you want to take on, that's a green pool cleanup, quoted after a photo, and then weekly service so next April is uneventful.