Hotel pool filters: backwashing, sand changes and how many hours to run them

Backwashing reverses the flow through a sand filter so water lifts the bed and carries trapped dirt out to drain. You do it when the pressure gauge rises above its clean reading, and stop when the sight glass runs clear. Run the filter long enough for the whole pool volume to pass through once, and change the media when backwashing no longer restores a low clean pressure.

The water is dull, the chlorine reading looks fine, and the plant room door has not been opened since the season started. Chemistry gets the attention because it is measured every day; the filter is what the water actually passes through, and nobody has looked at its gauge in weeks. This article walks the plant room: how a sand filter works, how to read the gauges, how to backwash safely, how to set running hours, where the backwash water goes, when to change the media, and how air gets in. If water quality is your wider concern, start with the pool health regulation as a checklist for water, staff and records.

What does a hotel pool filter do, and what can it not do?#

A sand filter traps suspended particles: the dirt, skin cells, sunscreen and floc that make water look dull. It does not kill anything, and it does not correct chemistry; disinfection and pH are a separate job done in the same water.

The mechanism is simple. Water enters the top of the vessel, passes down through a bed of graded sand or glass, and the particles are caught in the top few centimetres of the bed. Clean water leaves through the laterals at the bottom and returns to the pool. Everything else in this article follows from that one picture.

What the filter cannot do matters just as much. It does not remove dissolved matter, it does not disinfect, and it cannot compensate for low chlorine, wrong pH or high cyanuric acid. A perfectly clean bed will still leave water cloudy if the chemistry is wrong.

Turbidity is the filter's report card. The operator measures it every day with the other Annex 4 parameters, against a limit of 5 units as SiO2 or Jackson, or 0.5 NTU/FNU, under the Ministry of Health's Regulation on the Health Principles for Swimming Pools (opens in a new tab), Resmî Gazete 6 March 2011, No. 27866, Annex 4. A rising turbidity with a healthy gauge points you away from the filter and toward the water itself, which is the subject of finding the cause of cloudy or green pool water.

The regulation defines turnover time as the time needed for the total pool volume to pass once through the filtration system (Article 4), but it sets no turnover time, no filter type, no running hours and no backwash rule. That silence is where the plant room's own written discipline has to live. Your designer's specification and the filter maker's manual are the authority, not a habit.

A hotel is not a villa. The same vessel and pump that serve four bathers a day at a villa may face hundreds at a hotel, and bather load, not pool volume, is what fills a bed. A schedule copied from a villa does not transfer. The regulation's scope is pools open to the public; where a specific hotel pool sits in that scope is a question for your provincial health directorate, which inspects pools, pool water and pool chemicals monthly (Article 12).

How do you read a pool plant room: gauges, valves and flow?#

The pressure gauge on the filter is the main instrument: it shows how loaded the bed is. Read it on a clean bed, write the number down, and treat the maker's stated rise above that reading as your backwash trigger.

With a gauge before and after the filter you read the difference across the bed, which is the cleanest signal. With a single gauge, record the reading immediately after a backwash and rinse, when the bed is known to be clean, and compare everything to that. As the bed loads, resistance rises, pressure in the vessel rises and flow to the pool falls. The pool does not announce this; the gauge does.

The trigger is the maker's number, not a habit. The filter manual states the rise above clean pressure at which you backwash; write that figure into your procedure and never substitute a number remembered from another plant.

The multiport valve has six positions: filter, backwash, rinse, waste, recirculate, closed. Know the positions before you touch the handle, and never turn the handle while the pump is running, because the pressure can damage the valve seat and the laterals. The flow meter tells you whether the pump is delivering its design flow, and the sight glass tells you when backwash water has run clear; both are read, not guessed.

One trap: a blocked pump strainer basket produces low flow exactly like a dirty filter, but the filter gauge stays low instead of climbing. Check the basket before you backwash.

The log holds it together: date, time, gauge before, gauge after, minutes backwashed, who did it. The provincial health directorate inspection checks analysis record books and results (Article 12), and your own log is what turns a gauge reading into a decision.

How do you backwash a sand filter, step by step?#

Backwashing reverses the flow so water pushes up through the bed, lifts it and carries the trapped dirt out to drain. You stop when the sight glass runs clear, then rinse before returning the valve to filter.

Step 1: note the gauge reading and the time before you change anything, so the effect of the backwash can be measured. Step 2: switch the pump off before moving the multiport valve, then set the valve to backwash. Step 3: start the pump and watch the sight glass; the first water out is dark, and that is the dirt leaving the bed.

Step 4: run until the sight glass runs clear, and do not keep going past the maker's stated maximum, because you wash the graded bed out of the vessel and down the drain. Step 5: stop the pump, set the valve to rinse, run briefly to settle the bed, and send that first dirty water to waste rather than back to the pool. Step 6: stop, set to filter, restart, and record the new gauge reading next to the old one. That pair of numbers is the whole point of the exercise.

Step 7: backwash one filter at a time on a multi-filter plant, and prefer hours without bathers, because flow to the pool drops while a filter is out of service.

If the gauge returns to its high reading within a day, the bed is channelled, the media is spent, or the pump is delivering more than the bed can take. Backwashing again will not fix any of the three.

How many hours should a hotel pool filter run?#

Long enough for the whole pool volume to pass through the filter at least once a day, and longer when the bather load is high. The hours are arithmetic, pool volume divided by the filter's design flow, not a figure borrowed from another hotel.

The arithmetic: pool volume in cubic metres divided by design flow in cubic metres per hour gives the hours for one full turnover. The design flow comes from the pump and filter maker's plate and the pipework, not from an estimate. The regulation defines turnover time (Article 4) but sets no value for it, so the number you must meet is the one your designer specified and your maker supports. Write it into the plant procedure so the night shift and the day shift run the same pool.

A full day: the load arrives during the bathing day, so the cleaning happens during and after it. Many plants run continuously through the season; if yours does, record that as a decision with a reason, not as a default nobody remembers making.

A quiet day: the temptation is to shorten the hours and save power. If you do, take a turbidity reading and a gauge reading before and after the change and keep them. If turbidity climbs, the hours were too few, and you have the evidence.

The night: filtering overnight is when the pool has no bathers and the water can be polished. It is also when a burst pipe or a dry balance tank does damage unnoticed, so somebody has to look at the plant during those hours.

Bather load is the variable that decides everything. A hotel with hundreds of bathers in a day loads a bed far faster than a villa with four, and a heatwave or a children's session can double the load in an afternoon. Record the hours actually run, not the hours planned; the gap between the two is where most pool problems start.

Where does the backwash water go?#

We found no national text that says where hotel pool filter backwash water may be discharged. The Ministry of Health pool regulation and its annexes are silent on it, so the answer comes from your local water and sewerage authority's discharge rules and from how your hotel is connected.

What we checked: the pool regulation (Resmî Gazete 6 March 2011, No. 27866) sets water quality, inspection, chemical and cleaning duties, and says nothing about where backwash water goes. We found no national rule that fills the gap.

Who decides: the water and sewerage authority for your province sets what may enter the sewer and on what conditions, and your discharge permit and connection type decide what applies to your plant. Why it matters: backwash water carries the dirt you just removed plus a chlorine residual. Sending it to a garden, a stream or a rainwater line is a different act from sending it to the sewer, and may be treated differently.

Measure it: meter or estimate the volume per backwash and keep it in the log with the gauge readings. A number you can show is worth more than an argument later. Ask before the season, not during it; a written answer from the authority is worth more than a verbal assurance from a contractor, and it settles the question for the whole plant team. This is one of those questions where your own case decides, so confirm the rule with your authority and your environmental adviser.

When should the sand or glass media be changed?#

Change the media when backwashing no longer brings the clean-bed pressure back down, when the bed has channelled or hardened, or when the maker's service interval is reached. Separately, the regulation requires the pool to be emptied and given a general cleaning at least once a year (Article 8).

The signs: the gauge returns to its high reading within hours of a backwash, the backwash water never runs clear, sand appears in the pool, or the bed is clumped and calcified when you open the vessel. Sand or glass media is a choice for the maker's specification and local supply, not for a slogan; either way the grade and the bed depth must match the vessel, or the filter will not perform.

The job itself: isolate, drain, open the vessel, inspect the laterals and standpipe, remove the old media, clean, refill with the correct grade and depth, reassemble, then backwash to waste until clear before returning to filter. It is a crew and a skip, not a shovel and an afternoon.

The regulation puts other items on the same list. The pool is emptied and given a general cleaning at least once a year (Article 8); children's pools have their own water treatment plant and are emptied, cleaned and disinfected once a month (Article 9); the drain grate is kept closed (Article 11). Only Ministry-licensed disinfectants and pool chemicals may be used, stabilised chlorine compounds only in outdoor pools (Article 14), and the chemical store must hold enough personal protective equipment, which the inspection checks (Article 12). Laboratory reports sent to the operator are kept for one year (Article 6); keep them with the plant log, not in a separate folder nobody opens.

Put the media change and the annual empty into the hotel preventive maintenance plan and the winter closing checklist, so the work happens in the quiet weeks rather than in August.

Why does a pool filter take in air, and what are the other common faults?#

Air almost always enters on the suction side, before the pump: a low balance-tank level, a leaking strainer lid or union, a worn valve O-ring, or a vortex in the tank. The pump then runs noisy, the gauge bounces and flow to the pool falls.

Suction-side leaks do not show as water on the floor, because the pump pulls air in rather than pushing water out. Look at the strainer lid gasket, the unions and the valve stems, and check them with the pump running. Low water level or a vortex in the balance tank lets the pump draw air; raise the level, check the baffle, and watch the strainer basket for a swirl of bubbles. After any work on the vessel, vent the air out before returning to filter: an air pocket shows as a bouncing gauge and, on some valves, a hiss at the air release.

Other faults worth knowing: a blocked pump strainer (low flow, low gauge), a valve left on recirculate (no filtration at all), a broken lateral (sand in the pool), a worn pump seal, a closed return valve. What looks like a filter fault but is not: persistent cloudiness with a correct gauge and clear backwash water is usually chemistry or flow, not the bed. Check the water parameters, as covered in daily pH and chlorine care, and the delivered flow before you open the vessel.

What to do next#

Open the plant room today and write down three things: the clean-bed gauge reading after a backwash and rinse, the maker's stated rise above it that triggers the next backwash, and the design flow from the pump and filter plates. Those three numbers turn a vague instruction into a one-page procedure the whole shift can follow, and they give you the evidence to compare against the daily turbidity reading. Then settle the discharge question with your water and sewerage authority in writing, and put the media change and the annual empty into the maintenance calendar so they land in the quiet weeks.