ROUTINE CARE
Looking after the pool in heavy rain
Heavy rain does two things at once — it dilutes the chlorine and washes dirt in — so test and correct the water within 24 hours of the rain stopping, before algae gets a start.
Rainwater is soft and slightly acidic, so one heavy night pulls both pH and alkalinity down, dilutes the chlorine below 1 ppm, and washes dust, pollen and soil off the surrounds into the pool. That is why green water here almost always appears after the rain, not during it.
Before a storm
Clear away chairs, umbrellas, planters and anything loose from around the pool. Blown into the water they damage liners and tiles.
Do not lower the water to make room for the rain. Pools are designed to overflow; a pool with the level down is far more at risk from groundwater pressure.
The evening before, bring chlorine up to the top of the range, about 3 ppm, so there is something in reserve when it gets diluted.
If you have a cover or slats, close them to keep the debris out.
In a strong wind, leave the cover open instead. The wind drags it and wrecks the track and the motor.
Within 24 hours of the rain stopping
Net out the floating debris first.
Clear the skimmer and pump baskets. After a storm they are usually packed solid enough to choke the flow.
If the level is above the middle of the skimmer, set the multiport valve to waste and run the pump until it is back to normal.
Run a full test. After heavy rain, pH and alkalinity usually fall together.
Bring alkalinity back to 80–120 ppm first.
Then set pH to 7.2–7.6.
Bring chlorine back to 1–3 ppm.
Run the pump for at least 12 hours straight. What the rain washed in takes longer than usual to filter out.
Check the pressure gauge the next day. Backwash if it is 8–10 psi over the clean reading.
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