We get two leaf seasons, not one
Live oaks drop in spring, right as the water warms and algae wakes up. Everything else drops in the fall. So the two heaviest debris loads of the year land exactly when chemistry is least forgiving.
Add pecans, crepe myrtle blossoms, and oak catkins, and a pool under trees can take on more organic material in a week than it sees the rest of the year combined.
Why debris stains so fast
A wet leaf sitting on plaster releases tannins into a tiny pocket of water directly against the surface. Chlorine in the bulk water never reaches it at full strength. Within a few days you have a leaf-shaped brown mark that a brush will not remove.
Acorns are worse: they are dense, they sink instantly, and they sit in the deep end and in corners where the cleaner never goes.
What actually prevents it
Net the surface before debris sinks — floating leaves are a two-minute job, sunk leaves are a vacuum job, and stained leaves are a chemical job.
Empty skimmer and pump baskets and the cleaner bag far more often during leaf season. A packed basket kills flow, and low flow means poor circulation exactly when you need it most.
Keep chlorine at the higher end of your CYA-appropriate range through the drop, because every leaf in the water is consuming it.
If a stain has already set
Organic stains often lift with a targeted treatment and correct balance, and they are far easier to remove in the first few weeks than after a season.
Metal and mineral stains are a different animal and need a different product. Guessing wrong can set a stain permanently, which is why identifying the stain type comes first.
