Guidance

Typical Pool Problems


This chart brings together practical advice from PWTAG's book, Swimming Pool Water but arranged so as to address common problems faced by pool operators. It should ideally be used in conjunction with the book; material in Technical notes and information may also be useful.

Possible reasons

  1. Under-dosing of acid
  2. pH correction agent (CO2 or acid) storage tank may be empty
  3. No sample stream flow to automatic control
  4. ph controller may be fouled, out of calibration or faulty

Actions

  1. Adjust pH by dosing acid automatically; or if manual, increase testing and dosing frequency
  2. Check adequate supplies of pH correction agent
  3. Check the flow to the controller
  4. Clean/calibrate/replace sensor

Possible reasons

  1. Over-dosing of acid
  2. An interruption to sensor sample stream flow may cause inaccurate readings
  3. pH sensor may be fouled, out of calibration or faulty

Actions

  1. Stop dosing acid and if necessary consider dosing pool with sodium carbonate
  2. Check the flow to the controller
  3. Clean/calibrate/replace sensor

Possible reasons

  1. Dosing erratic
  2. Electrical, electromagnetic or radio interference may be causing the sensor reading to fluctuate
  3. Water not buffered by alkaline content

Actions

  1. Check dosing accuracy and frequency
  2. Seek technical advice
  3. Raise alkalinity by dosing with sodium bicarbonate

Possible reasons

  1. Alkalinity too high

Actions

  1. Increase acid dosing and/or dilute the pool with fresh water

Possible reasons

  1. Result of initial leaching of alkaline salts from concrete – balance tank, channels etc

Actions

  1. Accept it for the first few months and then it should drop off.

Possible reasons

  1. Water treatment plant inadequate or under-performing
  2. Filter ineffective: possible breakthrough of bed due to ineffective or inadequate backwashing
  3. Disinfection failure: hardness salts coming out of solution due to high alkalinity
  4. High calcium hardness
  5. Entrained air in water turning cloudy when disturbed
  6. Over-dosing of coagulant
  7. Ineffective filtration
  8. Coagulation ineffective
  9. Check for a pattern to the problem. For example, is it only during periods of heavy use? Does it clear after backwashing?

Actions

  1. Check specification and if necessary reduce bather loading. Check pool plant operation for restricted turnover, blockage, valve partially closed etc
  2. Check filter differential pressures and flow rates; inspect bed. If inspection reveals problem with the under drains or ineffective backwash flow, these need to be resolved by specialists. Otherwise, backwash thoroughly and maintain bed henceforth in accordance with manufacture requirements
  3. Check disinfection dosing, free chlorine and pH levels
  4. Control calcium hardness
  5. Check air release on filters – operate manually if necessary to release trapped air. Check for air being drawn into the system on the suction side of the pump, eg through the strainer gasket
  6. Check coagulant dosing is continuous and at low levels
  7. Check filter and bed
  8. Check coagulation regime

Possible reasons

  1. Algal growth – may be green dark green (almost black) and red-brown. Algae are caused by effects of UV (sunlight); also poor hydraulics, mixing and turnover
  2. Disinfectant residual may be too low

Actions

  1. Raise free chlorine concentration to 5mg/l overnight; scrub discoloured areas vigorously; vacuum or brush algae from surfaces
  2. Adjust chlorination (but also check water distribution and turnover)

Possible reasons

  1. Bacterial growth, biofilm

Actions

  1. Check circulation, raise free chlorine concentration to 5mg/l overnight, scrub walls. Adjust chlorination (but also check water distribution and turnover)

Possible reasons

  1. Combined chlorine too high beacuse of bather pollution
  2. Free chlorine too high
  3. pH value too high
  4. pH too low (nitrogen trichloride being produced)
  5. A build-up of organic material in overflow channels and/or balance tanks can also contribute to the problem

Actions

  1. Reduce bather load and ensure pre-swim hygiene is observed
    Adjust to set range for the pool
    Lower pH
    Increase to set range. Check form of combined chlorine using DPD 2 and 3: if mainly dichloramine, consider
  2. Increasing fresh water dilution
  3. UV treatment
  4. Superchlorination - Cleaning of overflow channels and balance tanks should be part of periodic maintenance (if practical)

Possible reasons

  1. Pollution levels too high
  2. Sunlight (UV breaks down free chlorine)
  3. Turnover reduced, hydraulics poor, filter dirty and flow levels reduced
  4. The disinfectant sensor may be fouled, out of calibration or faulty

Actions

  1. Reduce bather loading pre-swim hygiene is observed
  2. If it's a outdoor pool or one with large glazed areas, consider cyanuric acid dosing to ptevent chlorine loss
  3. Check filter, flow rates, strainer and values
  4. Check that the dosage contro and delivery system are operating normally. Clean/calibrate/replace the sensor

Check that the power supply to the dosage pump is turned on and there is power available
Check for airlocks in the chlorine pump head and delivery tubing
Check also the suction/discharge valves for contamination and the delivery tubing for leakage
Ensure that the dosage controller set point (if the controller is at or above set point, dosage will stop). The set point may require adjustment.
For erosion feeder systems: ensre that the dosage controller is turned on and has power
Check that th solenoid value is working correctly

Possible reasons

  1. The disinfectant sensor may be fouled, out of calibration or faulty
  2. A lack of sample stream flow may be causing incorrect readings
  3. The system may be siphoning due to contamination of the dosage pump valves or pressure retention (anti-siphon) valve
  4. The solenoid valve may be stuck open and delivering disinfectant continuously

Actions

  1. Check that there is no restriction to the sensor sample stream. Check that the dosage control and delivery systems are operating normally and clean/calibrate/replace the sensor
  2. Re-test and confirm the reading diluting the pool water first with non chlorinated water on a 2:1 basis then double the result. If the disinfectant level is outside minimum requirement, the pool must be closed until within range.If necessary, reduce disinfectant levels by dilution or sodium thiosulphate
  3. Check the dosage pump suction and discharge valves for contamination, as well as the diaphragm of the pressure retention (anti-siphon) valve for contamination
  4. For erosion feed systems: check that the solenoid valve is operating correctly

Possible reasons

  1. Bed of filter dirty through infrequent backwashing
  2. Too high levels of coagulant

Actions

  1. Check and improve backwash regime; inspect filter bed for contamination, consider refurbishment of underdrains and media
  2. Check coagulant dosing rates and quantities

Possible reasons

  1. Water too hard

Actions

  1. Check Langelier/Palin balanced water test and adjust pH, alkalinity and hardness according to findings

Possible reasons

  1. Chlorine levels too high

Actions

  1. Look for initial flash of colour when introducing DPD to drop of water in test cell. Take a further test diluting pool water with water containing no chlorine

Possible reasons

  1. Ineffective air circulation in pool hall

Actions

  1. Check air handling, dampers, filters and automatic controls; check levels of fresh air introduction

Possible reasons

  1. TDS too high

Actions

  1. Dilute with fresh water

Possible reasons

  1. Iron salts coming out of solution

Actions

  1. Check pH, water balance and coagulation. Consider full physical analysis of source water and pool water

Possible reasons

  1. Underdrain system in filters failed

Actions

  1. Check filter bed for signs of sand loss , uneven distribution and fissures. Replace underdrains and media