PEBBLECRETE / MATERIAL LIBRARY
Salt chlorinators and cement-based pool finishes: guidance for specifiers and operators
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What a salt chlorinator does and does not do in a pool with a cement-based exposed-aggregate finish, which water values to test and target, and what to watch during start-up, around metal fittings and in the records.
A salt chlorinator makes chlorine from dissolved salt. It does not balance the water, and its output percentage does not measure the free chlorine in the pool. We recommend salt chlorination for PebbleCrete finishes, because the chlorine level stays steadier and pH drifts upward rather than downward. On a cement-based exposed-aggregate finish such as PebbleCrete, the operator’s job is the same as with any chlorine source: test regularly, keep pH, alkalinity, calcium hardness and free chlorine within the agreed targets, and record each action, bearing in mind that pH tends to drift upwards and needs watching because of the scale risk.
What a salt chlorinator does
Water containing dissolved salt passes through an electrolytic cell, which makes chlorine in the circulating water while the cell is running. Units control their output in different ways, so confirm with the equipment supplier how the unit works.
Two points are often misunderstood:
- The output percentage is a setting, not a measurement. A display showing 60% is a selected output setting, and what it means depends on the equipment. It does not show the free chlorine level in the water. Only a water test does that.
- Making chlorine does not manage water balance. pH, total alkalinity and calcium hardness still have to be tested and adjusted.
Size the unit at the design stage. An undersized unit can run at 100% and still fall short, which leaves the operator adding chlorine by hand. In hot climates with strong sun and heavy bather loads, ask the equipment supplier to confirm that the unit has enough spare capacity for the pool volume and expected use.
Why ph drifts up, and why it matters
Pools with salt chlorination commonly show a gradual rise in pH. Upward drift suits a cement-based finish better than low pH does. Left unchecked, though, high pH combined with calcium in the water makes scale more likely. Scale can form on the finish, especially at the waterline, and inside the chlorinator cell.
The answer is small, frequent corrections rather than large, occasional ones. On a PebbleCrete finish:
- The target pH is 7.6–7.8. A working range of 7.2–7.8 is acceptable, but below 7.6 the water slowly begins to draw on the cement matrix, so aim for 7.6–7.8.
- Do not over-correct. Below about 7.6, the water slowly begins to draw on the cement-based finish, and faster if alkalinity or calcium hardness is also low. Pushing pH too low to fight scale swaps one problem for another.
- Dose with care. Add chlorine into the balance tank or, failing that, the skimmer. Add acid and other chemicals as the product instructions, the equipment instructions and the approved treatment procedure direct. Never pour any chemical onto the finish.
What to test, and the targets
Clear-looking water is not a test result. Use suitable test equipment and follow its sampling instructions.
| Parameter | Target for a PebbleCrete finish | Note |
|---|---|---|
| Free chlorine | 1–3 ppm | Our target for every system, including salt chlorination, not a universal assurance of adequate disinfection. Commercial pools must also meet local disinfection requirements |
| pH | 7.6–7.8 (working range 7.2–7.8) | Affects chlorine activity and the finish |
| Total alkalinity | 80–120 ppm | Buffers pH against sudden swings |
| Calcium hardness | 200–400 ppm | Read together with pH and alkalinity |
| Salt | Within the chlorinator manufacturer’s range (typically 3000–4500 ppm) | Low-salt and standard systems differ |
| Cyanuric acid (if used) | 30–50 ppm | Higher levels reduce chlorine’s effectiveness and change how free chlorine readings should be interpreted |
These are the values we ask for on a PebbleCrete finish. Where local regulations set different disinfection requirements, comply with them; the pH, alkalinity and calcium-hardness targets protect the finish and remain the values we ask for, and keeping pH on target is essential.
Read the values together, because one acceptable reading does not prove the water is balanced. Follow the testing schedule set for the pool, its equipment and local requirements, and test more often in hot weather and at busy times. Check alkalinity, calcium hardness and the LSI at regular intervals as well as chlorine and pH. Testing only chlorine and pH is a common gap.
In tropical climates, heavy rain can dilute salt and alkalinity, and evaporation followed by topping up shifts the balance again. Test after heavy rain or large top-ups, and know what the top-up water contains.
The start-up month
A new cement-based finish continues to cure under water after filling. Follow the agreed start-up programme in full before switching to normal operation.
- Do not add salt at first fill. Wait 28–30 days. Then follow the written start-up instructions and the chlorinator manufacturer’s requirements before commissioning the unit.
- Brushing: widely used start-up programmes call for brushing the whole pool daily through the first month, with filtration running continuously. Many programmes call for brushing twice a day in the first week. Follow the schedule issued for the pool.
- During start-up, chlorinate only as the programme directs, always dosing through the balance tank or skimmer. Chlorine added straight onto the surface will mark it, and correcting the water afterwards will not undo the damage. This applies to granules, tablets and liquid. Never broadcast chlorine across the pool or let a tablet rest on the surface.
- When salt is added, follow the chlorinator manufacturer’s method. Do not leave undissolved salt sitting on the finish.
Record the fill date, every test result, everything added and anything observed. Clear water alone does not show that the pool is ready to use.
Metal fittings and staining
Salt water can speed up corrosion of some metals. A corroding light ring, grille or fixing can leave rust trails down the wall and across the floor. Iron or copper in the water can also cause colour changes.
- Ask the manufacturers to confirm that ladders, light rings, grilles, fixings and other metalwork are suitable for chlorinated salt water.
- Electrical bonding and earthing of the cell and metalwork are for the electrical designer and installer to resolve under local regulations.
- Test the filling water, including for metals, and keep the results.
- Inspect fittings regularly and deal with early rust before it spreads.
If a stain appears, investigate it before treating it. Note whether it is linked to a fitting, a water source or a recent treatment, and whether something has been deposited on the surface or lost from it. Do not experiment with strong acid or abrasive cleaning. Clean the chlorinator cell as its manufacturer directs, away from the pool, and never rinse cleaning acid into the pool or onto the finish. Agree a diagnosis and repair scope first, because repeated cleaning will not remove a source that is still active.
Keep a useful record
A written record turns separate readings into a history that can be interpreted. Include:
- date, time, test method and readings, with pH kept separate from values in ppm
- the reading before each correction, the action taken and the reading afterwards
- chlorinator setting changes, salt additions and cell cleaning
- rain, top-ups, unusual bather loads, nearby building work and circulation interruptions
- dated, located photographs of any new deposits, marks or roughness
When the pool passes to a new operator, hand over the finish identification, approved care instructions, equipment information and start-up record.
Frequent topping up or salt that keeps falling may mean the pool is losing water. The finish is decorative. It is not structural repair or waterproofing, so a leak must be traced in the structure, pipework, joints and penetrations.
Planning and expectations
As a planning figure, an exposed-aggregate pool finish is generally expected to serve for 15–20 years. This is an industry estimate, not a warranty term. Where an individual pool falls within or outside that range depends on substrate preparation, application quality, water chemistry and routine maintenance.
In Thailand: Pebble Pools (pebblepools.co.th), a separate company, offers salt-water pool systems.
Frequently asked questions
Can a salt chlorinator be used with a cement-based exposed-aggregate finish such as PebbleCrete?
Yes, and we recommend it. Chlorine is produced continuously, so free chlorine stays steadier within 1–3 ppm, and pH tends to drift upward rather than downward, which is the direction a cement-based finish prefers. The operator still has to test and balance the water, and salt is added only after the 28–30-day start-up period.
Does a salt chlorinator remove the need to test the water?
No. Making chlorine does not measure free chlorine or manage water balance. Regular testing of chlorine, pH, alkalinity, calcium hardness and the other values above is still essential.
Can salt be added as soon as the pool is filled?
No. Wait 28–30 days, then follow the written start-up instructions and the chlorinator manufacturer’s requirements.
The chlorinator is at 100% but free chlorine is still low. What should be checked?
First, measure free chlorine, pH, salt and cyanuric acid. Then check the cell for scale following the chlorinator manufacturer’s instructions, and ask the equipment supplier whether the unit has enough capacity for the pool. The output setting is not a reading, so trust the water test rather than the display.
Photographs and screen colours are illustrations. Confirm colour and texture with a current physical sample viewed wet and an approved on-site mock-up.
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This article provides general technical guidance, not a design, installation or safety instruction for a specific pool. Every project depends on its structure, substrate, waterproofing, water conditions and local regulations. Refer to the current PebbleCrete technical documents: the Technical Data Sheet and the Installation Overview are available online, and the Safety Data Sheet and the full Method Statement are issued on request. Confirm structural, waterproofing, electrical and installation decisions with qualified professionals. PebbleCrete supplies the material only; unless agreed otherwise in writing, substrate preparation and application are carried out by the owner’s applicator, who is responsible for that work. Nothing in this article limits your statutory rights.