Hydrolab Minisonde 5 (including Surveyor with GPS system)


Hach LDO™
Since 2002, Hach has established itself as the premier provider of Luminescent Dissolved Oxygen technology, and only Hydrolab Series 5 sondes feature Hach LDO technology – designed, manufactured, and supported by Hach in Loveland, Colorado.

• No membranes
• Calibrations that last
• Superior accuracy
• Compact housing allow complete integration into any sonde – DS5X, DS5, or even MS5

• Calibrations that last without drift means that deployments will last longer, reducing frequency of trips to the field for maintenance, saving you time and money
• No membranes so concerns about air bubbles, 24-hour membrane relaxation, and the art of maintenance are a thing of the past
• Does not consume oxygen so passive fouling will not affect DO readings
• Best accuracy because solid, defendable data is the ultimate goal
• Designed, manufactured, and supported by Hach Environmental, the experts in LDO technology, so all your questions can be addressed locally

Product Data:

Range:  0 to 60* mg/L
* Exceeds Maximum Natural Concentrations
Accuracy: ±0.1 mg/L at <8 mg/L
±0.2 mg/L at >8 mg/L
±10% reading >20 mg/L
Resolution: 0.01 mg/L


What is Hach LDO and how does it work?
The Hach LDO sensor cap is coated with a luminescent material. Blue Light from an LED strikes the luminescent chemical on the sensor. The luminescent chemical instantly becomes excited. As the excited chemical relaxes, it releases red light. The higher the oxygen concentration, the less red light given off by the sensor cap. The red light is detected by a photo diode. The time it takes for the chemical to return to a relaxed state is measured.

The oxygen concentration is inversely proportional to the time it takes for the luminescent material on the sensor cap to return to a relaxed state.

Between flashes from the Blue LED, a red LED of known intensity is flashed. The red LED acts as an internal standard for reference comparison to the red light given off by the luminescent sensor cap. This comparison allows the sensor readings to remain stable for long periods of time.

How long will the sensor cap last?
The sensor cap is a consumable item that Hach Environmental recommends replacing once per year.

What is the warranty on the Hach LDO sensor?
The LDO sensor is covered by our standard 2-year warranty. The consumable sensor cap is covered by a 1-year warranty.

Is a circulator required with the Hach LDO sensor?
No, because the Hach LDO sensor does not consume oxygen, it is not necessary to continually replenish the water sample around the sensor.

Will fouling affect the DO readings from a Hach LDO sensor?
Passive fouling will not affect the Hach LDO sensor because the sensor does not need to consume oxygen. However, active fouling, such as barnacles, that consumes oxygen itself will misrepresent the condition of the water around the sensor. Active fouling can be easily removed from the sensor by using the self-cleaning mechanism included with the Hydrolab DS5X.

What is the recommended calibration procedure for Hach LDO?
When calibrating Hach LDO, it is very important that the Temperature sensor and the LDO sensor cap have equilibrated in the same environment. This can be accomplished in any of the three calibration procedures (air saturated water, water saturated air, and known standard calibration), but Hach Environmental recommends the air saturated water procedure. Our tests have shown this procedure to be the most consistent and replicable.

The air saturated water calibration can be accomplished without the use of expensive and clumsy pump mechanisms. Instead, please refer to the instruction sheets for a full description of the method, which utilises a 2-litre plastic bottle, (e.g., an empty soda bottle) and our standard calibration cup.


The Hydrolab Conductivity sensor uses four graphite electrodes in an open cell design to provide extremely accurate and reliable data with virtually no maintenance.

• Design based on four graphite electrodes in an open cell design
• The probe measures the current between 2 electrodes held at a fixed potential; additional electrodes are used to compensate for any fouling of the electrode surfaces
• Sensor measurements used to derive Salinity, Total Dissolved Solids, and Resistivity

• Reduces measurement error due to environment – sediment falls to the bottom of the cell, and bubbles rise to the top. Measurements are reliable in any condition.
• Easily maintained between deployments by cleaning with a Q-tip or cotton swab

Product Data:

Range:  0 to 100 mS/cm
Accuracy: ± (0.5% of reading + 0.001 mS/cm)
Resolution: 0.001

FAQ Conductivity

What is the difference between Conductivity and Specific Conductance?
Specific conductance is the scientific term for conductivity values that have been compensated to 25°C.

How is Salinity measured using this sensor?
Salinity is a value that is derived mathematically from the conductivity readings. Hydrolab instruments use an algorithm from the USGS Water Supply Paper 2311 titled "Specific Conductance: Theoretical Considerations and Application to Analytical Quality Control" as the default. Users also have the option to choose the algorithm described in section 2520B of "Standard Methods for the Examination of Water and Wastewater (pdf)".

How do you determine Total Dissolved Solids (TDS)?
Total Dissolved Solids is also derived mathematically from the conductivity readings. The default factor for TDS calculations is 0.64 however this can be user defined if historical data for a specific water body dictates the need for a different factor.


The Hydrolab pH sensor uses glass bulb and refillable reference electrode for reliable data from a sensor that is easily maintained and long-lasting.

• KCl impregnated glass bulb is permeable to hydrogen ions; reference filled with 3M KCl and has a porous Teflon junction. Salt bridge is formed between the two, and a potential is measured.
• Choice of standard or integrated refillable reference
• A special low ionic strength reference electrode is available for measuring waters with conductivities below 200 μS
• Optionally paired with ORP sensor

• Reference electrode is easily refilled in seconds – independent of the pH sensor
• pH sensor does not need replacement when reference electrode is depleted; simply refill the reference

Product Data:

Range: 0 to 14 pH units
Accuracy: ±0.2 units
Resolution: 0.01 units


How often will I have to rebuild the pH reference?
The frequency with which a pH reference needs to be refilled depends on the deployment conditions of the sonde. The more frequently that a user logs readings, the more frequently the reference will need to be refilled.

What are these salt pellets in my reference junction?
The salt pellets are 99.99% KCL and during deployment they dissolve, keeping the reference solution at a desired molarity level.

What is the difference between a Standard Reference and an Integrated Reference?
The Standard Reference used with a pH sensor is installed in a separate sensor port on the DataSonde or MiniSonde. The Integrated Reference is incorporated into a single sensor and will allow the sonde to be configured with another sensor that would not otherwise be possible. Both sensors have the same specifications, and both will provide measurements of equally high quality. The MiniSonde and DataSonde are available with either option, and the Quanta is available only with the Integrated Reference.

When would I need a Low Ionic Strength reference junction?
If the water body that is being measured has the possibility of having a conductivity value of 0.200 ms/cm or lower, we recommend the use of the Low Ionic Reference.

Depth/Vented Level

Hydrolab offers high-stability, custom-made pressure sensors with four range options.

• Depth measures absolute hydrostatic pressure from an internal diaphragm • Optimised for depths down to 10 m, 25 m, 100 m, or 200 m

• Vented level (0 to 10 m) uses a sealed dryer attached to a fixed cable that provides compensation for changes in barometric pressure.

Product Data:

Range: 0 to 10 m (Vented Level) 0 to 25 m 0 to 100 m 0 to 200 m
Accuracy: ±0.003 meters ±0.05 meters ±0.05 meters ±0.1 meters
Resolution: 0.001 meters 0.01 meters 0.01 meters 0.1 meters

FAQ Depth:

What is the Vented Level sensor?
The Vented Level sensor provides extremely accurate water level measurements at depths to 10 m. This sensor requires that the sonde be equipped with a fixed, vented cable that allows the level measurement to be compensated for the barometric pressure above the water.

Turbidity: Self-Cleaning
Hydrolab's Self-Cleaning Turbidity sensor measures from 0 to 3000 NTU and includes a user-programmable cleaning system to remove any fouling or debris that could otherwise affect readings.

• ISO 7027 compliant
• User-programmable self-cleaning system can perform up to 10 cleaning cycles before each reading
• Accurately measures up to 3000 NTU

• Fixed parking position ensures consistent data collection after each cleaning cycle
• 3000 NTU range allows Turbidity tracking even during rain storms or other events that could cause abnormally high readings
• Exceptional linearity even in high NTU environments
• Utilises small aperture technique to reduce false readings from particulates and other debris

Product Data:

Range: 0 to 3000 NTU
(compared to StablCal):
±1% up to 100 NTU,
±3% from 100 to 400 NTU
±5% from 400 to 3000 NTU
Resolution: 0.1 NTU from 0 to 400 NTU;
1 NTU for >400 NTU
Temperature Coefficient: 0.05%/C

Sensor housing:

Stainless steel:
Standard housing for typical fresh water applications and depths to 200 M.

Corrosion-resistant housing for use in aggressive saline environments such as oceans, bays, and estuaries. Rated to depths of 50 M.

Consult with your sales representative to determine which sensor best fits your needs.

FAQ Turbidity: 4-Beam

How is the Quick Cal-Cube™ used to check the calibration of the 4-Beam Turbidity sensor?
The Quick Cal-Cube™ is the simplest method available for checking the calibration of the 4-Beam Turbidity sensor. After calibration with primary standards, the value of the optional Quick-Cal Cube™ secondary standard, if used, must be determined and recorded for each individual instrument. The Quick-Cal Cube™ value is determined by removing the storage/calibration cups, wiping the optical areas, both sensor and cube, clean and dry with a non-abrasive, lint free cloth, and placing the ceramic glass cube into the turbidity sensor's optical area. Align the Quick-Cal Cube™'s pin with the turbidity sensor's recessed hole and, for optimum repeatability, rotate the Quick-Cal Cube™ clockwise to remove mechanical play in the pin/hole. To test for drift between primary calibrations, reinstall the Quick-Cal Cube™.

Hydrolab's ORP sensor uses a simple platinum band that donates or accepts electrons to monitor chemical reactions, quantify ion activity, or determine the oxidizing or reducing properties of a solution.

• The state of the reaction is measured by the potential developed between and inert noble metal electrode (platinum) and a reference electrode (same reference for pH) • Compliant with SM2580 B

• The ORP is greatly influenced by the presence or absence of molecular oxygen. Low redox potentials may be caused by extensive growth of heterotrophic microorganisms. Such is often the case in developing or polluted ecosystems where microorganisms utilise the available oxygen. Low ORP is another relative measure for biological oxygen demand.

Product Data:

Range: -999 to 999 mV
Accuracy: ±20 mV
Resolution: 1 mV


What is ORP?
ORP, or Oxidation-Reduction Potential, (also known as Redox) is a measurement of the voltage at an inert electrode, reflecting the extent of oxidation of the water sample. The more positive the ORP of a solution, the more oxidized are the chemical components of the water (less positive indicates less oxidized, or more reduced).

Why would I want to measure ORP?
ORP measurements are used to monitor chemical reactions, to quantify ion activity, or to determine the oxidizing or reducing properties of a solution. The ORP is greatly influenced by the presence or absence of molecular oxygen. Low redox potentials may be caused by extensive growth of heterotrophic microorganisms. Such is often the case in developing or polluted ecosystems where microorganisms utilise the available oxygen. Here again, is another relative measure for biological oxygen demand; low ORP


For complete water quality sonde set-up and real time monitoring, the Surveyor is a simple and rugged handheld display that is designed specifically for use with the Hydrolab DS5X, DS5, and MS5.

• Rugged and dependable NEMA 6 case with handstrap
• Displays data in real-time or can store up to 375,000 measurements
• Oversize screen with backlight allows data to be viewed in any conditions
• Available with optional GPS and Barometric Pressure capabilities
• Available in English, French, or Spanish

• Designed specifically for use in severe field conditions, the Surveyor can take a beating on land or in the water and still deliver your data
• Allows the user huge flexibility – the Surveyor can be used for real time data collection or graphing and it can be used for setting up and downloading log files
• Complete set-up capability allows users to leave their laptops in their offices
• GPS option automatically integrates latitude and longitude coordinates with water quality data
• Barometric Pressure option makes Dissolved Oxygen calibration simple, and can be logged with water quality data

• Memory: 375,000 measurements
• Battery Supply: Rechargeable Nickel Metal Hydride
• Typical Battery Life: 12 to 16 hours
• Size: 11" x 4" x 5"; 27.9 cm x 10.2 cm x 3.8 cm
• Weight: 2 lbs; 0.9 kg

Water Quality Sondes FAQ

How deep can these sondes go?
The Series 5 and Series 4a sondes are all built to withstand depths to 225 meters. The Quanta and Quanta-G are built to withstand depths to 100 meters.

Can the same unit be used in fresh and salt water applications?
Yes. Hydrolab sondes and sensors are built to operate in either fresh water or salt water applications.

Is any assembly required for a Hydrolab sonde?
No. The Hydrolab sondes will arrive at your facility completely assembled and ready for use. Hydrolab does, however, recommend calibration in your environment and using your procedures before deployment.

How long can I deploy my instrument?
Deployment length depends on battery life and bio-fouling. Battery life is affected by the number of the parameters being measured and the frequency of measurement. Fewer parameters and less frequent measurements require less power, and therefore can have longer battery life. Bio-fouling depends on the environment in which the unit is deployed. Biological growth is more prevalent in warmer climates and more active waters. Fortunately, the effects of bio-fouling can be greatly reduced by using the Hydrolab DS5X to periodically and automatically clean the sensors.

How frequently can I take a reading if using a log file?
As delivered from the factory the smallest interval is 30 seconds, however by changing the setup the minimum interval can be as low as 5 seconds.

How do I store a unit over the winter?
Clean the instrument and place one ounce of tap water in the storage cup. Place the instrument in a location that will not be exposed to temperatures below freezing or above 50°C.

What do I need to do when deploying my unit after being stored for a long period of time?
Complete the following checklist:

DataSonde 5X

Do I need to purchase a Self-Cleaning Turbidity sensor with the DataSonde 5X?
No. The DataSonde 5X is available with or without the Turbidity sensor.

How often should I change the wiper?
Hydrolab's brush is designed to retain its effectiveness for a long period of time because our fibres are very strong and our design will not allow them to separate over time. However, in extremely active environments, the brush itself can become fouled and reduce its effectiveness. Hydrolab includes 4 replacement brushes with the maintenance kit for the DataSonde 5X, so you will not incur any additional costs if a change is needed.