Swimming pool water treatment

What the programme covers

Pool water has two jobs to get right, and they are tested and managed separately. Disinfection is the chlorine. Balance — pH, total alkalinity and calcium hardness — decides whether that chlorine works and whether the water is quietly attacking the grout, the fittings and the heater. A treatment programme holds both at once, on a schedule, with the paperwork to show it.

• Disinfection — free chlorine held at the level your licence conditions name, from slow-dissolve chlorine tablets, sodium hypochlorite or both, matched to how the pool is used
• Water balance — pH, total alkalinity, calcium hardness and cyanuric acid tested and corrected in the right order: alkalinity first, then pH, then hardness
• Daily testing support — DPD No. 1 and phenol red comparator kits and reagent refills for the register the licence requires, on a standing delivery so the comparator never runs dry (see pool test kits)
• Scheduled testing — typically monthly, giving you independent numbers to file alongside the daily register
• Laboratory certificates — bacteriological and clarity results through a HOKLAS-accredited independent laboratory, the evidence FEHD's own guide points to (see laboratory testing)
• Chemical supply — chlorine, pH and alkalinity correction, algaecide, clarifier and test reagents delivered across Hong Kong, on a standing delivery if you want one (see pool chemicals)
• Automatic dosing and monitoring where the pool justifies it — sensors for pH, ORP and free chlorine, dosing to hold the water in range and an alarm when a reading drifts (see real-time monitoring & dosing)
• A dated report after every visit — in plain language, filed next to the register, readable by a committee or an inspector

What happens on site

1. Survey. Pool volume, plant room, filtration turnover, how the pool is dosed today, and what your own licence and letter of requirements say — FEHD can stipulate non-standard conditions for an individual pool. We test the fill water too, because calcium hardness is set mainly by what comes out of the tap.
2. Set the programme. Chlorine source chosen for the pool, not off a shelf: an indoor pool should generally run unstabilised on liquid chlorine, a high-turnover pool suits sodium hypochlorite on a dosing pump, a small clubhouse pool without daily plant-room attendance may do better on tablets in a feeder. Target bands are agreed with the pool operator and written down.
3. Scheduled testing. pH, free and combined chlorine, total alkalinity, calcium hardness and cyanuric acid, with a plain statement of what to correct and in what order.
4. Laboratory sampling. Samples taken at the right point, at bather depth and away from an inlet, handled correctly on the way to the laboratory, analysed by a HOKLAS-accredited independent laboratory and returned as a formal dated certificate.
5. Chemical delivery. To your usage, not the shelf — liquid chlorine loses strength in storage, so it is ordered to turnover rather than stockpiled, and reagents are replenished at the rate a daily-tested pool consumes them.
6. Report. A dated written report after every visit: what was tested, what it read, what was done and what the operator should do next.

The numbers a licensed pool has to hold

Under the Swimming Pools Regulation (Cap. 132CA), a pool that the public can use, or that is operated by a club, institution, association or other organisation, must hold a licence from the Director of Food and Environmental Hygiene. The only exemption FEHD publishes is a pool serving not more than 20 residential units with no public access — so almost every estate clubhouse, hotel and club pool is a licensed pool. The licence sets working numbers, and the chlorine and pH duties are continuous: at all times bathers are in the water, not at the morning test.

FEHD accepts a pool water test report from an accredited laboratory as evidence that the plant can hold the standard, and the government told the Legislative Council in 2023 that FEHD inspects licensed pools monthly while they are open. Your own licence and letter of requirements are the final word for your pool; the full set of obligations, including the lifeguard and record-keeping conditions, is set out in swimming pool licence requirements in Hong Kong.

Why pH decides what your chlorine does

The most common pool failure we see is not too little chlorine. It is chlorine that is present, measurable and idle. Free chlorine exists in a strong, fast-killing form and a weak one, and pH sets the split between them: at pH 8, only around a quarter of your free chlorine is in the strong form. A test kit reads both forms together, so the register looks fine while algae pressure builds in the corners and the operator doses more. Correcting pH is usually far cheaper than the extra chlorine poured in to compensate for not correcting it.

The slower loss is the fabric of the pool. Water that is low in pH, alkalinity or hardness etches plaster and grout and corrodes ladders, light fittings and heat exchangers. Water that is high in all three clouds and deposits scale, fastest inside the heater. Neither failure announces itself; both are priced at renovation time in tens of thousands rather than in bags of chemicals. The mechanism and the correction order are in pool water balance: pH, alkalinity and hardness.

Then there is the tablet catch. Every trichlor tablet adds about 0.6 mg/L of cyanuric acid for every 1 mg/L of chlorine, and nothing in normal operation removes it. Left untested it accumulates until the chlorine kills slowly whatever the reading says. That is why the programme tests stabiliser, and why we will tell you to stop buying tablets when yours is already high — see chlorine tablets vs liquid chlorine and cyanuric acid and chlorine lock.

What Gotech does — and does not — do at a pool

We are a water treatment company. At a pool that means the chemistry, the testing, the chemicals and the laboratory paper trail. It does not mean the deck.

• We do not provide lifeguards. The licence fixes a minimum number of qualified life-saving attendants at the pool edge and the signed duty logs behind them, retained for at least 90 days. That is the pool management company's responsibility, and we do not offer it.
• We do not clean or staff the pool. Vacuuming, skimming, tile and deck cleaning, changing rooms, attendants and opening hours stay with the pool operator.
• We work alongside the pool management company. Their attendants take the daily DPD reading with kits and reagents we supply; their register and our scheduled results sit in the same file; our report tells both of you what to correct and in what order. One contractor for the water, one for the pool, and paperwork that agrees with itself.

One boundary case is worth naming. Where a water storage tank fills the pool, FEHD's licence conditions require its inside thoroughly cleansed every three months while the pool is in use. That is water treatment work, and we do it: see Potable water disinfection.

Who this is for

Estates and clubhouse pools. The decision is made by an owners' committee or managing agent who must justify the spend to residents, so quotations are written so they can be tabled at a meeting and reports are in plain language residents can read. The same committee usually owns fresh water tanks and cooling plant too — see water treatment for estates & pools.

Hotels and clubs. The pool and spa sit under the same contract as the cooling towers and hot water services, work is scheduled around occupancy rather than around us, and reports are formatted for group compliance files and brand audits. Several of our hotel contracts have run continuously since 2015 — see water treatment for hotels.

Gotech has treated Hong Kong water systems since 1982. Client names are kept private; reference lists are shared with quotations on request.

Frequently asked questions