Importance of measuring turbidity in the pool

Category: Pools | Tags: #  
Is your water
really crystal clear?
Hazy water can have a huge impact on the pool features, not only for the health effect but also for the overall pool presentation.
General rules tend to prescribe water clarity very clearly.

The National Sanitation Foundation standard for water clarity in pools is 0.5 nephelometric turbidity units (NTU). At times of peak bather loads, the turbidity is allowed to increase to 1.0NTU but must return to 0.5NTU within 6 hours (NSPF 2005).

The National Sanitation Foundation standard for water clarity in pools is 0.5 nephelometric turbidity units (NTU). At times of peak bather loads, the turbidity is allowed to increase to 1.0NTU but must return to 0.5NTU within 6 hours (NSPF 2005).

Usually the procedure follows the measurement that falls out of specification, the pool manager needs to identify the cause of turbidity.

In most cases, when you can identify the cloundiness by visual test (eye) the values are already too high, and sometimes can be too late. 

The causes of turbidity are most commonly:

How to measure turbidity in a swimming pool?

Turbidity is a measurement of the cloudiness or haze of the water. Swimming pool, hot tub, and spa water can have varying degrees of cloudiness from the indiscernible to very noticeable when the bottom of a pool cannot be seen. The cloudiness or haze can be a symptom of a variety of problems from biological forms including algae and bacteria to precipitates such as calcium carbonate that will appear at elevated pH levels. Back flushing, filter cartridge replacement, adding flocculants, or a simple pH adjustment can sometimes resolve the increase in water turbidity. The remedy is determined by the cause of the increase in turbidity. 

The turbidity of a swimming pool, hot tub, or spa should be kept low at a value of 0.5 FNU/NTU or less.

Turbidity serves as a useful indicator of filter performance and can signal potential issues with filtration and flow rates, filter breakthrough or poor backwash routines. It is recommended that filtration systems are operated to continuously achieve filtrate turbidity less than 0.2 Nephelometric Turbidity Units (NTU).

Pool Line ISO Portable Turbidity Meter
The HI987134 is a high accuracy portable turbidity meter. The meter is supplied complete with AMCO-AEPA-1 primary turbidity standards used for calibration and performance verification. The HI987134 meets and exceeds the requirements of the ISO 7027 Method for turbidimetric measurements.
  • Fast Tracker™ – Tag Identification System (T.I.S)
  • USB for data transfer
  • Up to four-point calibration
The HI987134 Pool Line Precision ISO Turbidity Portable Meter is specially designed for water quality measurements, providing reliable and accurate readings, even within low turbidity ranges. The instrument is based on a state-of-the-art optical system which guarantees accurate results, assures long term stability, and minimizes stray light and color interferences. Periodic calibration with the supplied standards compensates for any variations in intensity of the LED light source. The 25 mm round cuvettes composed of special optical glass guarantee the repeatability of turbidity measurements.

Features at-a-glance

Ratio Measurement Mode

The HI987134 measures turbidity using the ratio method with a 90° and 180° light detector for more accurate measurements. Turbidity measurements can be made in the 0.00 to 1000 FNU range.

Multiple reading modes

Normal measurement, continuous measurement, or signal averaging measurement are reading modes available.

ISO Compliant

The HI987134 meets and exceeds the requirements of ISO 7027 method for turbidity measurements by use of an infrared LED light source.


The HI987134 has a powerful calibration function that compensates for variation in light intensity. The calibration can be done using the supplied calibration solutions or user-prepared standards. A two, three, or four-point turbidity calibration can be performed by using the supplied (<0.1, 15, 100, and 750 FNU) standards. Calibration points can be modified if user-prepared standards are used.


1 Primary Turbidity Standard – The AMCO AEPA-1 supplied standards are recognized as a primary standard by the USEPA. These non-toxic standards are made of styrene divinylbenzene polymer spheres that are uniform in size and density. The standards are reusable and stable with a long shelf life.

Fast Tracker™

For advanced field applications, the HI987134 is equipped with Fast Tracker™ – Tag Identification System (T.I.S.) that makes data collecting and management simpler than ever. Fast Tracker™ allows users to record the time and location of a specific measurement or series of measurements using iButton® tags near sampling points for quick and easy readings. Each iButton® tag contains a computer chip with a unique identification code encased in stainless steel.

GLP Data

The HI987134 features complete GLP (Good Laboratory Practice) functions that allow traceability of the calibration conditions. Data includes calibration points, date, and time.

Data Logging

Up to 200 measurements can be stored in the internal memory and recalled at any time.

Data Transfer

For further storage or analysis options, logged data can be downloaded to a Windows® compatible PC using the USB or RS232 port and the HI92000 software.

Backlit Graphic LCD Display

A graphic LCD display provides an easy to understand, user-friendly interface. All messages are in plain text making them easy to read.

Turbidity Range Turbidity Resolution Turbidity Accuracy Turbidity Repeatability
1.0 to 9.99; 10.0 to 99.9; 100 to 1000 NTU
0.1; 0.1; 1 FNU
±2% of reading plus 0.1 FNU
±1% of reading or 0.01 FNU, whichever is greater

With sufficient disinfection very immportant is to take in consideration factors sun, bathers load and adjust your automatic system acordingly.

Nives Vinceković Budor,


Subscribe to our Newsletter