Cloudy or green pool water at a hotel: finding the cause and the order of correction

Green water is algae growing because chlorine is not holding; cloudy pool water at a hotel is particles the filter cannot catch. Check the pump, then the filter, then the chemistry, then the bather load, in that order. Close the pool when you cannot see the main drain or a laboratory result fails.

It is ten in the morning, the pool deck is filling, and the water has gone from clear to milky overnight. Someone suggests a bucket of chlorine and someone else suggests flocculant, and both are guessing, because nobody has looked at the filter gauge yet. This article gives you a diagnosis order, a closure rule and a record format, so that the next event takes hours instead of days and does not repeat two weeks later.

What is the difference between cloudy, green, white and foamy pool water?#

Each symptom points to a different part of the system: green is biology, cloudy is particles, white is usually chemistry or air, and foam is organic load. Treating the wrong one costs a day and the fault returns.

Green water is algae that was already present starting to grow because free chlorine is no longer holding, not a sudden infection arriving from outside. Cloudy or milky water is fine material the filter cannot catch: flow too fast, filter media channelled, or chemistry that keeps particles suspended. A white haze, or scale crusting on the tiles, is a hardness and pH problem, and no amount of algaecide will touch it.

Foam that persists for hours is organic load, sunscreen, cosmetics and sweat, or detergent carried in on swimwear; foam that collapses in minutes is usually just air from a return inlet or a waterfall. And clear water is not safe water: the eye cannot see microbiological quality, which is why the regulation requires laboratory analysis rather than a visual check. The decision rule for the whole article: name the symptom before opening any container.

Why does hotel pool water turn green?#

Green water is algae growing because chlorine is consumed faster than it is added, or because the chlorinated water never reaches part of the pool.

Chlorine demand scales with people. For example, a hotel pool that takes two hundred bathers in a day carries sweat, sunscreen and urine that consume free chlorine far faster than a family pool with four swimmers, so a dosing routine that worked in June can fall behind in August without anything being broken.

Cyanuric acid, the stabiliser that shields chlorine from sunlight, also holds chlorine in a form that kills more slowly once it builds up over a season. The regulation requires daily testing of pH and chlorine; cyanuric acid should be tested regularly, often weekly, because high levels reduce disinfection efficacy. Dead spots start the bloom: corners, ladder recesses, steps, the balance tank and the zone behind the return inlets where flow does not reach.

Pump hours matter too. A pump cut to a short daily window to save energy leaves the water stratified and the chlorine sitting in one place. Shock treatment kills what is in the water but does not remove the cause; with a weak filter and poor circulation the algae returns within days. Algae already settled on walls and floor has to be brushed off and vacuumed out, because chemical alone does not remove the film that protects the cells underneath. For the daily measurement routine behind all of this, see measuring and correcting pH and chlorine each day.

Why is the pool water cloudy or white?#

Cloudy water is material the filter cannot remove, and the usual cause sits upstream of the chemistry, in the filter and the flow.

Filter media has a life. Sand that has channelled, compacted or simply aged lets fine particles pass straight through to the pool. A pressure gauge that does not move after a backwash is a warning sign, because it means the gauge, the valve or the media is no longer telling you the truth about the filter.

Flow rate cuts both ways: too fast pushes particles through the bed, too slow leaves the whole pool under-circulated and the turnover time too long. Chemistry can keep particles suspended as well: high pH, high total alkalinity and high calcium hardness all hold fine material in the water column instead of letting it settle or be caught.

Flocculant gathers small particles into larger clumps the filter can catch, but it only works when the filter and the flow are already right. Added to a failing filter, it makes the water worse, not better. Oils from sunscreen and cosmetics form a film that clouds the water and feeds chloramines, so a cloudy pool after a busy weekend is partly a load story. Once the cause is fixed, clearing takes hours of continuous filtration; no product shortens that if the filter is the problem. For the filter side in detail, see backwashing, sand changes and how many hours to run the filter.

In what order should you check a hotel pool?#

Pump, filter, chemistry, then bather load. The first two decide whether any chemical you add will do anything at all.

Pump first: is it running, for how many hours, and is the flow actually arriving in the pool? Feel the return inlets and watch the skimmer draw rather than trusting the control panel. Then filter pressure, compared against the clean baseline recorded after the last backwash: a rise means loading, a sudden drop can mean a broken valve, a bypass or a channelled bed.

Backwash and rinse must be done properly and at the right interval, because a filter that is never washed and a filter that is washed every day both fail in the end. Check valves and the balance tank: a partly closed valve or a low balance tank starves the pump, and everything downstream reads as a chemistry problem when it is not.

Only then the chemistry: free chlorine, pH, cyanuric acid and total alkalinity, in that sequence, with the same test method each time so the numbers are comparable. Last, the load: how many bathers used the pool, whether a group arrived at once, and whether that matches what the plant was designed to handle.

When should you close the pool, and what do you tell guests?#

Close when you cannot see the main drain, when free chlorine will not hold, or when a laboratory result fails. The last one is not a judgement call.

The regulation sets the mandatory case. If a microbiological result fails, the pool is closed until a new sample passes; if a chemical result fails, the operator receives a written warning, and the pool is closed if the repeat sample also fails (Regulation on the Health Principles for Swimming Pools, Resmî Gazete, 6 March 2011, No. 27866, consolidated text on mevzuat.gov.tr (opens in a new tab), viewed 4 November 2026).

Beyond the legal minimum, the operator's own triggers should include: no visibility of the main drain, a strong chloramine smell, a faecal or vomit incident, and foam that will not clear. Name the role that decides in the written procedure, not the person, so the decision does not depend on who is on shift.

What guests hear should be short and factual: a sign at the pool and a line at reception with the expected reopening time, with no diagnosis and no chemistry. A partial closure of one section is usually harder to police than a full one, and guests move into the closed area anyway. Write down the closure time, the readings that triggered it and who signed, because that record is what an inspector reads first and what tells you later whether the cause was fixed. For the wider duties, see the health regulation as a checklist for water, staff and records.

How do you correct green or cloudy water, step by step?#

Correct in the same order you diagnosed: restore circulation and filtration, then chemistry, then remove what has settled, and only then reopen.

No doses belong in an article. The product label and the trained pool water operator set the quantity, and a hotel pool is dosed by measurement, not by a rule of thumb carried over from a home pool. Use only products approved for pool water in your market, and keep the label and safety data sheet on file.

Shock treatment raises free chlorine quickly to burn out the demand; it needs the pool empty of bathers and the filter running throughout. Algaecide comes after the shock, not instead of it, and brushing walls, steps and corners first is what lets the chemical reach the algae rather than the film over it.

Flocculant settles particles to the floor, and a slow vacuum to waste then removes them; brushing without vacuuming only lifts them back into the water. Run filtration continuously until the water clears, then backwash, and expect the filter to load faster than usual for a day or two.

Why does the problem come back, and what should you record?#

It comes back because the correction treated the water and not the cause, and the record is what turns one event into a fixed cause.

The usual root causes repeat: filter media past its life, pump hours cut to save energy, cyanuric acid creeping up across a season, one dead spot nobody brushes, and bather load above what the plant was designed for. The regulation already requires a testing rhythm: temperature, pH and free chlorine at least three times a day, first before the pool is used and then every four hours; colour, turbidity and cyanuric acid daily; total alkalinity weekly (Regulation on the Health Principles for Swimming Pools, Resmî Gazete, 6 March 2011, No. 27866, Annex 4, consolidated text on mevzuat.gov.tr (opens in a new tab), viewed 4 November 2026).

It also requires the latest temperature, pH, free chlorine and microbiological results to be posted where users can see them, and laboratory reports kept for one year for inspectors. Add what the regulation does not ask for: the day's bather count, the pump hours, each backwash, the closure and reopening times, and the name of the person who signed.

Review the log monthly rather than only when something fails: two closures in one season with the same reading point to a single cause worth fixing in the plant, not in the water. If a guest was affected during the event, the pool entry belongs in the incident record as well as the pool log, so the two accounts agree.

What to do next#

Write the check order on one page, pump then filter then chemistry then load, and post it in the plant room this week. Then set up the log with one line per day: readings, bather count, pump hours, backwashes, closures and a signature. The parts fit together as one loop: the symptom tells you where to look, the order tells you what to fix first, the closure rule protects the guests while you do it, and the record is what stops the same failure returning next month.