Water Treatment

Before filling: check the water and its delivery

Do not introduce dirty or contaminated water into a newly finished pool. Check the source, storage tanks and delivery hoses before the application date, and clean away construction debris. Appearance alone does not establish water quality: keep the relevant test results and agree the filling and startup plan with the project team.

See the filling-water lesson and site photographs ↗

Watch the earlier PebbleGlass filling example ↗

Understanding pool-water care

Water care is part of caring for the finish. Clear-looking water is not a substitute for test results. Keep a written operating record so that changes can be understood over time.

Parameter	What it tells you
Free chlorine	The chlorine available to disinfect the water. Interpret the reading alongside pH and any cyanuric acid present.
pH	A unitless measure of acidity and alkalinity. It affects chlorine activity and the water’s interaction with pool materials.
Total alkalinity	The water’s capacity to resist changes in pH; it is different from pH itself.
Calcium hardness	The dissolved calcium level. Read it together with pH and alkalinity when assessing risks of calcium deposits or damage to cementitious surfaces.
Cyanuric acid	A chlorine stabiliser that changes how chlorine readings and disinfection requirements should be interpreted.
Metals	Iron or copper in the water may be relevant when investigating colour changes or staining.

Use appropriate test equipment and follow its sampling and testing instructions. Record the result before corrective treatment, the action taken and the subsequent reading. This gives the next operator useful context and helps identify repeated problems. Operating targets depend on the pool, treatment system, applicable requirements and approved care guidance.

A salt chlorinator produces chlorine. Its output percentage is an equipment setting, not a measurement of chlorine in the water. Check actual free chlorine and pH readings and adjust operation under the equipment instructions. UV or ozone equipment also does not justify reducing disinfectant levels without an approved operating basis.

A new cementitious finish needs its agreed startup programme, including filling, brushing and water monitoring. Arrange suitable water and a responsible operator before finishing begins. Keep the startup record with the handover documents, then follow the routine care programme after the startup period.

Operating targets

These are the values we ask for on a PebbleCrete finish. They sit inside the ranges published by the National Plasterers Council and PebbleTec, with one deliberate difference: we ask for pH at the upper end rather than the middle.

Parameter	PebbleCrete target	Why this value
pH	7.6 – 7.8	The value we ask for. A working range of 7.2 – 7.8 is acceptable, but below 7.6 the water starts to satisfy its acid demand from the cement matrix that holds the aggregate.
Free chlorine — liquid chlorine or trichlor	1 – 3 ppm	Dosing is intermittent, so the level moves between additions. Short excursions to 3 ppm are acceptable.
Free chlorine — salt chlorinator	1 – 2 ppm	Chlorine is generated continuously, so a lower steady level does the same work.
Total alkalinity	80 – 120 ppm	The buffer that keeps pH from moving. Without it, pH control becomes a daily argument.
Calcium hardness	200 – 400 ppm	Per National Plasterers Council guidance for cement-based finishes. Our aggregate contains no calcium; the cement matrix does.
Cyanuric acid	30 – 50 ppm	Above roughly 50 ppm the stabiliser begins to suppress the chlorine you have already paid for.
Langelier Saturation Index	−0.3 to +0.3	Read the parameters together. A single acceptable reading is not evidence that the water is balanced.

If pH is held where it should be, the rest of the programme is far more forgiving. If it is not, no other parameter compensates.

Chlorination: match the target to the system

The two chlorine figures above are not a contradiction. They describe different delivery methods, and the choice of method changes what else you have to watch.

Liquid chlorine and trichlor

Dosing is intermittent, so aim for 1 – 3 ppm. Trichlor is the common choice across Southeast Asia and it works against the finish perfectly well — it is simply the more demanding option, because every tablet adds cyanuric acid and pushes pH down. Watch the stabiliser as it accumulates and move to liquid chlorine when it approaches 50 ppm.

Salt chlorination

We recommend it. Chlorine is produced continuously, so 1 – 2 ppm is enough, and pH tends to drift upward rather than downward — which is the direction this finish prefers. Specify a chlorinator with headroom: an undersized unit runs at 100% and still falls short, and the operator then compensates with hand dosing.

Salt is not added at first fill. Wait 28 – 30 days, then follow the written start-up instructions for the system and the chlorinator manufacturer’s requirements.

Never add chlorine directly onto the finish

This one is absolute, and it applies to every form of chlorine — granules, tablets and liquid alike. Chlorine introduced straight onto the surface will mark it, and the damage is not reversible by correcting the water afterwards. Add chlorine into the balance tank, or failing that the skimmer, so that it is diluted and circulated before it ever reaches the finish. Never broadcast it across the pool and never let a tablet rest against the surface.

The first month

The surface continues to cure under water. Brush the whole pool daily through the first month, and keep filtration running continuously. Start-up programmes often call for brushing twice a day in the first week; follow the schedule issued for your pool.

Record the fill date, every test result, everything added and anything you notice. Water that looks clear is not by itself evidence that the pool is ready for use.

A note on practice in Southeast Asia

Filling water drawn from a lake, a river or a well can arrive at pH 5.5. Trichlor is then added without correcting pH, and site testing often covers only chlorine and pH — not alkalinity, hardness or the index that ties them together. A cement-based finish treated that way can be visibly damaged within six months. This is the single most common cause of premature wear we see, and it is entirely preventable.

Where the cement matrix is etched, the aggregate stands further out and the surface feels rougher; left long enough, aggregate begins to shed. A finish applied at its nominal 10 mm has reserve to be polished back once the water is corrected — but correcting the water is the part that has to happen.

Keep a useful operating record

Record	Useful detail
Test readings	Record the date, time, test method and readings; keep pH separate from values expressed in ppm.
Treatment changes	Record products and amounts added, equipment adjustments, filter work and unusual water use.
Filling water	Identify the source and keep available test results, especially when investigating metals or staining.
Surface observations	Photograph new deposits, marks, roughness or cracks with a location and date.
Events	Note rain, topping up, unusual bather load, nearby building work and interruptions to circulation.

Review the record as a sequence. A single reading taken after corrective treatment may not explain what happened earlier. When handing the pool to a new operator, include the finish identification, approved care instructions, equipment information and the startup record.

Surface changes: investigate before repairing

A change in appearance needs investigation. Deposits, staining, roughness, cracks and hollow-sounding areas can have different causes and may require different responses. Begin by identifying what has changed and where it occurs.

Record when the change appeared, whether it is spreading, and whether there is water loss. Take an overall photograph and close-ups, and gather water-test records, treatment changes and any recent building work. Note whether the problem is isolated to a fitting, edge or particular water level.

Distinguish material deposited on the surface from material lost from it. Check whether a suspected stain is associated with a fitting, a filling-water source or a previous treatment. Cracks and detached areas require examination of the layers beneath the visible finish. These observations narrow the investigation; they do not prove a cause on their own.

Repeated surface cleaning will not solve an unresolved source of staining or a fault beneath the finish. Agree the diagnosis and repair scope before using strong chemicals, aggressive abrasion or draining the pool. A local repair may remain visible because of material variation, exposure and the age of the surrounding finish; agree appearance expectations before work begins.