Filters backwash when pressure rises and media gets replaced on a schedule. Days until the next service come from the install date plus the cycle length — with a pressure-rise trigger too.
The example
Sand installed, 36-month cycle.
| A | B | |
|---|---|---|
| 1 | Item | Value |
| 2 | Install + 36 mo | — |
| 3 | Days left | → countdown |
The formula
The formula:
How it works
How it works:
- Media life: sand ~3–5 yr, DE recharge each backwash, cartridge ~1–3 yr.
- Days remaining =
install_date + cycle_months×30 − TODAY()— a live countdown. - Also backwash on pressure: when gauge rises ~8–10 psi over clean, it’s time.
- Flag service due with IF on either the date or the pressure trigger.
Educational use only — not chemical-safety or professional advice. Pool chemical dosing varies by product strength, water chemistry, and local rules. Always follow the product label, add chemicals to water (never water to chemical), test before and after, and never mix chemicals. Verify with a professional.
Try it: interactive demo
Install date and cycle (months).
Variations
Pressure trigger
Backwash now?:
Service-due flag
Within 30 days:
Next due date
From install:
Pitfalls & errors
Media differs. Sand, DE, and cartridge have very different cycles.
Pressure too. Backwash on a ~8–10 psi rise, not just the calendar.
Not advice. Follow equipment specs for media and pressure.
Practice workbook
Frequently asked questions
How do I track filter media replacement in Excel?
When do I backwash?
How long does filter media last?
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