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Why a paper card in 2026
Because pool decisions happen standing at the equipment pad with wet hands, a chemical jug in one arm, and a phone that's inside the house. The six numbers on this card end the re-figuring: how many gallons, what chlorine level is actually right for your stabilizer, when the filter pressure means "clean me."
The two numbers people get wrong
The chlorine target: it scales with CYA (about 7.5% of it), so the card computes yours instead of printing a generic "1–3 ppm" that's wrong for half of pools. And the filter pressure: the service point isn't a universal PSI, it's ~25% above your clean baseline — which is why the card records both.
Make it a set
The card pairs with the water test report card for weekly checkups — card on the wall for the constants, analyzer in the browser for this week's readings.
Frequently asked questions
What numbers should every pool owner have written down?
Pool volume in gallons (every dose depends on it), your chlorine target for your CYA level, pH and alkalinity ranges, pump schedule, and filter's clean pressure reading. Those six cover 95% of poolside decisions.
What is a normal filter pressure?
There's no universal number — it depends on your plumbing. What matters is YOUR clean baseline: note the PSI right after a filter clean, and service the filter when it rises about 25% above that. That's why the card has a spot for it.
Why write down the pool volume?
Because every chemical label doses per 10,000 gallons and every calculator asks for it. Measuring once and recording it beats re-estimating badly every season — a 20% volume error makes every dose 20% wrong.
Where should I keep pool information?
Tradition says taped inside the equipment-pad door or pump-house wall — it survives weather, phone battery, and being borrowed by whoever is watching the house. A phone photo of the card is a good backup.