Introduction
On the estates around Barreiro, Palhais, Santo António da Charneca and Coina, pools are frequently large. Not 30 or 40 m³ like an urban villa: 70, 90, sometimes 120 m³, built when land was plentiful and energy was cheap.
A large pool is not a normal pool with more water in it. It changes the physics of the problem — how long the water takes to pass through the filter, how fast a chemical correction distributes, what a dosing mistake costs — and almost every difficulty these owners describe comes from applying a 40 m³ pool's reasoning to a 90 m³ one.
This article is about the arithmetic of a large volume, and the three decisions that make the difference.
Turnover Time: The Number That Decides Everything
Turnover time is how long the pump takes to pass a volume equal to the pool's volume through the filter. It is worked out like this:
Turnover time (hours) = pool volume (m³) ÷ pump flow rate (m³/h)
A real example of the kind we find on estates:
| Pool A | Pool B | |
|---|---|---|
| Volume | 40 m³ | 90 m³ |
| Pump flow rate | 10 m³/h | 12 m³/h |
| Turnover time | 4 hours | 7.5 hours |
| Filtration hours/day for 2 turnovers | 8 h | 15 h |
Pool B has more than double the volume and a pump only 20% larger. It is the most common pattern in older estate pools: the pump was chosen from what was available, not from what the volume demands.
Practical consequence: pool B will never clear properly on 8 hours of filtration a day. It is not the treatment that is wrong — it is the time.
If you do not know your pool's real volume, start there: How to Calculate Pool Water Volume.
Chemical Inertia: Correct in Stages
In a large volume, a dose of corrector takes far longer to distribute. That has two consequences that generate errors.
The first: measuring ten minutes after applying gives a figure that means nothing. The product is still concentrated in one part of the pool.
The second, and more expensive: applying more product because "it did not work". In a 90 m³ pool, overdosing costs three times what it does in a 30 m³ one, and correcting an overdose costs more still.
The correct method at large volume:
- Calculate the dose for the real volume, not an estimate.
- Apply half the calculated dose.
- Filter for at least two to three hours.
- Measure again.
- Apply the rest, if needed.
It sounds slower and it is faster, because it avoids the overdose-and-correct cycle. See also How to Balance Pool pH.
💡 Dica Profissional
On an estate pool, measure the real volume once, with a tape measure, and write it on a sheet taped to the plant room door. It is the number that goes into every dosing calculation for the next twenty years, and it is the number almost nobody has right.
The Three Decisions That Count on a Large Pool
1. A variable-speed pump
On an estate pool this is probably the best investment available. The reason is mathematical: on a large pool the number of filtration hours needed is high, and a pump's electricity consumption does not vary linearly with speed — reducing speed reduces consumption far more than proportionally.
Translated: a variable-speed pump running more hours at low speed filters the same volume for a fraction of what a fixed-speed pump running fewer hours at full speed consumes. On a 90 m³ pool needing 15 hours of daily filtration, the annual difference is significant. See Variable-Speed Pumps.
2. A cover
On a large pool the exposed surface is large — and evaporation is proportional to surface, not to volume. An uncovered estate pool through an inland summer loses a considerable amount of water, and every top-up adds calcium hardness without removing anything.
A cover for a large pool costs more, and the return is proportionally greater: less evaporation, fewer top-ups, less hardness climb, less leaf fall, less disinfectant demand through reduced sun exposure.
3. A filter sized with headroom
If you are replacing the filter on an estate pool, this is the chance to size it for the real volume with headroom, instead of repeating the original undersizing. A larger filter backwashes less often and keeps the water more stable. See Pool Filter Types.
Well Water: Common on Estates
Many estates around Barreiro and Coina are fed from a well, and at large volume that has a specific consequence: filling a 90 m³ pool with well water is an enormous quantity of iron and hardness entering at once.
The protocol is the same as for any well-fed pool — analysis, pH correction, metal sequestrant and only then disinfectant — but the scale amplifies mistakes. A badly executed fill on an estate pool can stain 200 m² of lining.
We covered the full protocol in Well Water in Moita: How to Treat It, and it applies here in full.
Heating: The Sum That Changes on a Large Pool
The question always comes up on estates: is heating worth it?
The physics is unforgiving: the energy needed to heat water is proportional to volume, and evaporation losses are proportional to surface. On a 90 m³ pool with 45 m² of surface, both numbers are large.
Two practical conclusions:
Without a cover, heating a large pool is heating the garden. Most of an outdoor pool's heat loss is through surface evaporation. A cover is not an accessory to heating: it is the condition that makes it make sense.
The heat pump has to be sized for the volume. An undersized heat pump on a large pool runs permanently without ever reaching the target temperature. See Heated Pool: Consumption and Maintenance.
The Plan for an Estate Pool
| Frequency | Task | Note for large volume |
|---|---|---|
| Daily | Surface net | The surface is large: it takes longer |
| 2-3x/week | pH and free chlorine | Always measure at the same time |
| Weekly | Vacuum, brush, waterline | Consider a robot: on a large pool it saves hours |
| Weekly | Filter pressure vs reference | — |
| Monthly | Alkalinity, calcium hardness | Hardness climbs with top-ups |
| Seasonal | Opening, closing | Check turnover time at start-up |
| Annual | Pump, panel, sand overhaul | Replacements cost more: plan them |
Common Mistakes
Filtering the same hours as a small pool. The structural error of estate pools.
Not knowing the real volume. Every dosing calculation starts there.
Applying the whole dose at once. At large volume, correct in stages with filtration between them.
Heating without covering. Evaporation loss eats the investment.
Filling with well water without a protocol. Scale amplifies the error.
Frequently Asked Questions
How many hours a day should I filter a 90 m³ pool?
It depends on the pump's flow rate. Divide the volume by the flow rate to get turnover time, and multiply by two to three turnovers a day in the bathing season. With a 12 m³/h pump, that gives 15 to 22 hours — which usually means the pump is undersized.
My estate pool never really clears. Why?
The most frequent cause on large pools is insufficient filtration time for the volume, followed by filter sand at the end of its life. Neither is solved with more product.
Is a variable-speed pump worth it on a large pool?
It is probably the best-returning investment. On a pool needing many filtration hours, filtering longer at low speed consumes a fraction of what filtering less at full speed does.
How do I calculate a product dose for a large pool?
From the real, measured volume. And apply half the calculated dose, filter for two to three hours, measure again, and top up if needed. At large volume, mixing is slow.
Does it make sense to heat a 90 m³ pool?
Only with a cover. Without one, heat loss through surface evaporation makes heating a large pool economically hard to justify.
I have a well. Can I fill the whole pool from it?
Yes, with a protocol: prior analysis, alkalinity and pH correction, metal sequestrant, and only then disinfectant, with continuous filtration for the first 24 to 48 hours. At large volume, skipping steps stains a far bigger area.
Conclusion
On an estate pool, almost every problem is resolved with three numbers: the real volume, the pump's flow rate, and the turnover time the two produce.
Key points to remember:
- Turnover time = volume ÷ flow rate. It is the number that decides your filtration hours.
- Measure the real volume once and tape it to the plant room door.
- Correct the chemistry in stages, with filtration between them.
- A variable-speed pump and a cover: the two best decisions on a large pool.
- Heating without covering makes no economic sense at large volume.
If you have an estate pool in Barreiro, Palhais, Coina or Santo António da Charneca and have never known whether the equipment matches the volume, the on-site technical diagnosis measures the flow rate, calculates turnover time and tells you in writing how many hours you need to filter. It costs €45, deductible from your first month under contract.
