Handheld Servicing for OxyGuard Handy & YSI Pro Series

At Sterner UK we provide manufacturer backed servicing of OxyGuard’s Handy series and YSI’s Pro Series instruments, including the tried and test OxyGuard Polaris and YSI Pro2030.

From the unit arriving at our workshop, our team of manufacturer trained engineers inspect and service every handheld in line with the premier service expected from Sterner.    We conduct a dry test to ensure the probe is reading accurately, check the connections on the circuit board and every unit undergoes cross calibration with manufacturers certified reference probe.   Each probe undergoes renovation and once completed we will provide a Certificate of Calibration, essential for your on-site records and audit trails.

The manufacturers recommend that units are serviced annually.  This planned preventative maintenance helps to save on downtime & ensure the continued accuracy of your monitoring device.

If your handheld is beyond economical repair, we offer a part exchange scheme* on OxyGuard and YSI units, allowing you to trade in your old unit for a new one, with a saving of £100 off a new unit.

Contact David on 01463 250275 or email service@sterner.co.uk to arrange your service today.

NEW: OxyGuard Polaris C Dissolved Oxygen Meter

Hand-held oxygen and temperature meter with NFC and Bluetooth technology for automatic or manual upload to Cobalia

The Polaris C meter is a high-performance, low-cost and almost maintenance-free meter for measuring dissolved oxygen and temperature. The meter is sturdy, easy to use and has an extensive longevity making it  ideal for harsh conditions. Polaris C can store up to 2500 complete set of data, including time and date stamps. The logged data can be stored either manually or automatically with the possibility to group the data into categories.

The stored data can be uploaded directly to Cobália using Bluetooth technology*. Scan the Cobália NFC tag on the tank and all data will be uploaded to your “digital farm”. Tank specific data assigned to the tags will be stored in Cobália for analysis on temporal variation, generation of graphs and for multivariable analysis on performance.  The meter has a built-in self-check of all hardware, it compensates automatically for  barometric pressure and it has a notably short response time. With this meter, you get the high-quality associated with OxyGuard technology and a product that will serve you well for many years.

* Works only with Android at this time.

Key Benefits

  • High accuracy
  • Easy-to-do calibration
  • Automatic check of the hardware
  • Automatic compensation for barometric pressure and temperature
  • Water-resistant
  • Automatic or manual data logging of up to 2500 full sets of data
  • Bluetooth and NFC technology for direct upload to Cobália
  • Low power consumption: ~1000 hours
  • Immediate response time
  • Variable display options and unit use
  • Self-polarising and temperature compensating electrochemical probe
  • Long-term stability


  • Units of measurement: Oxygen: ppm (mg/L), % saturation. Temperature: degrees Celsius (°C), degrees Fahrenheit (°F)
  • Display: Graphical LCD display with variable backlight
  • Probe type: Electrochemical
  • Cable length: Standard 3 m. Available at any length up to 50 meters by request
  • Operating temperature: Probe: -5 to +45 degrees Celsius (°C) and +23 to +113 degrees Fahrenheit (°F). Meter: -20 to +60 degrees Celsius (°C) and -4 to 140 degrees Fahrenheit (°F)
  • Waterproof: Short-term immersion proof to 5m depth
  • Response time: To 90% in less than 20 seconds
  • Measuring range: Oxygen: 0-60 mg/L and 0-600 % saturation. Temperature: -5 to +45 degrees Celsius (°C) and +23 to +113 degrees Fahrenheit
  • Measuring accuracy: Oxygen: typically ± 1% of measured value. Temperature: ± 0.2 degrees Celsius/Fahrenheit (°C/°F)
  • Data logging capacity: 2500 sets of data with up to 99 data groups
  • Salinity compensation range: 0-50 ppt salinity. Manually set
  • Automatic check of: Probe function, meter function, cable and battery
  • Automatic compensation: Temperature and barometric pressure (0-7000 m a.s.l)
  • Dimensions meter: Length = 98 mm, diameter = 36 mm (Length: 3.86 in, diameter: 1.42 in)
  • Dimensions probe: Length = 159 mm, diameter = 22 mm (6.26 in, 0.87 in). With protection cap: Length = 176 mm, diameter = 29 mm (6.93 in, 1.14 in)
  • Power: 2 AA alkaline batteries
  • Battery life: 1000 hours use depending on settings and battery quality
  • Standard accessories: 10 membranes and O-rings, 50 ml electrolyte, cathode cleaning pad, tool, storage pouch

Choosing the right Dissolved Oxygen Meter

What Do I Need to Know Before Purchasing a Dissolved Oxygen Meter?

So, you've decided you need a dissolved oxygen meter to monitor oxygen levels for your fish pond, hatchery or sea site.   Perfect, here are some things for you to consider;

  1. What parameters do you want to measure? It sounds obvious when choosing a DO Meter, but is it just dissolved oxygen you want to measure.  For most trout ponds and hatcheries, dissolved oxygen and temperature are the key parameters to monitor.  Our aquaculture industry leading OxyGuard Polaris CPolaris 2 and YSI Pro20 DO Meters are perfect for ponds and hatcheries
  2. Is your water only fresh water? Ponds and Hatcheries are most commonly fresh water, but there are several which will have sea water, water with a saline content or even some tanks with fresh water and some with salt water.   Knowing the salinity of your water, can affect the dissolved oxygen reading on your meter and can even have an affect on the quantity of feed used and costs associated.  Our OxyGuard Polaris units, offer a manual salinity compensation.  If you need to monitor both dissolved oxygen and salinity, the YSI Pro ODO/CT is a single handheld instrument with allows you to measure dissolved oxygen, temperature and conductivity.
  3. What other parameters do you need to measure?  It's become very common to want to measure more than just dissolved oxygen and temperature in recent years, with a significant rise in measuring pH both in hatcheries and at sea.   For header tanks, Total Gas Pressure (TGP) has become important in addition to just dissolved oxygen.
  4. I'm needing to use a handheld monitor at sea. Our range of handhelds are ideal for use both on land based farms and at sea.   Our YSI Pro SOLO range is ideal for use on sea sites and challenging environments.   The YSI ProSOLO ODO/T offers a modern solution for dissolved oxygen and temperature, using optical probes, thus reducing maintenance, whilst the YSI ProSOLO ODO/CT monitors dissolved oxygen, temperature and conductivity.  You can read more about the YSI ProSOLO range here.
  5. How do I capture my data?  Pencil and paper are still popular, but somewhat old hat and can lead to data being "fudged".   The Polaris 2 range of DO and TGP Meters offer a USB download to Windows PCs, as do the YSI ProSOLO ODO/T and ODO/CT handhelds
  6. I want to monitor multiple parameters, what's the best way to do this?  This depends entirely on personal preference and your budget.   If you like the OxyGuard Handy range on instruments, then you need to be prepared to accept multiple instruments.   This has positives and negatives, positives being that the cost of servicing and repair can be less, and you can have multiple people taking different parameter readings.   The YSI Pro DSS offers multiple parameters, in a very customisable way.   The ProDSS with parameters from dissolved oxygen, ph, ORP, Turbidity, Ammonia, Ammonium, Nitrate, TDS (Total Dissolved Solids) and many more.
  7. I've chosen a meter, how do I look after it?  All our dissolved oxygen meters come with instructions for use and how to maintain, but we all break things.   At Sterner, our Service Centre of manufacturer trained and accredited engineers, provide annual servicing and calibration certification for OxyGuard and YSI instruments.

What's our most popular Handheld Meters? Our most popular meters for hatcheries and ponds is the OxyGuard Polaris, ideal for monitoring dissolved oxygen and temperature.   For sea sites, the YSI ProSolo ODO/CT measuring dissolved oxygen, temperature offers a robust and versatile meter for challenging environments.

Brewery: Incoming Water for Brewing

Incoming mains or borehole water would typically be filtered via an RO system for brewing liquor production and boiler feed. Microbreweries and craft brewers will often filter the incoming water with carbon cartridges to remove chlorine and other chemicals, which could affect the taste of the beer.

Brewery: Rough Filtration


Rough filtration is the removal of bulk solids such as grist and bulk yeasts. Process filtration often uses bags for this purpose as bags allow a high flow rate, remove a large volume of solids and are quick and easy to change out, making them economic to use. Bags are available with options of nylon mesh, polypropylene and polyester with traditional single-layer, extended life double-layer and high-efficiency multi-layer with Micro fibres incorporated for fine sediment removal. Bag filtration is commonly used to remove bulk solids, e.g. grist and bulk yeasts.

Oxygen Generation, containers solutions onsite

As Sterner approaches its 20th year in the UK and Ireland market place the industry desire for solutions to meet our customers challenges continues to grow.

This has been demonstrated only recently by the increase in demand for oxygen generation solutions for both freshwater and seawater applications, this technology has been adopted by Sterner through its association with Airsep corporation since the late 90,s with some of the original systems still offering critical life support for juvenile stocks.


At Sterner we can package any of our Standard Airsep oxygen generators with a multitude of
options to provide a turnkey solution for your oxygen needs.

We also have pre-configured containerised systems, which are designed to match the most common applications. Typical package systems consist of a Standard Airsep oxygen generator matched with a dedicted Kaeser air compressor. We also provide the option to integrate your containerised oxygen plant into an existing OxyGuard Commander Pacific system on site.

Through collaborations with valued customers this has expanded to seawater with turnkey oxygen generation and distribution systems delivering highly saturated O2 into sea pens for both life support and also improved production.

These systems vary in capacity and method of distribution dependent on site conditions and biomass and can be deployed as a containerised plug and play solution.

The current climate has also seen our containerised O2 systems deployed for back up to liquid supply for both traditional flow through and large RAS set ups to ensure continuity and peace of mind.

Sterner will undertake design, build and deployment for our oxygen generation packages all backed up with a service plan tailored to your individual needs



NEW OxyGuard Optical LDO Oxygen probe

OxyGuards new optical oxygen probe is developed in cooperation with world leading experts. Based on luminescence quenching of a sensor dye immobilized on a support foil it can be used for gas measurements as well as for dissolved oxygen (DO).

The presence of molecular oxygen quenches the luminescence, changing its intensity and lifetime fully reversibly. The measurement principle is very robust.  It shows virtually no interference to other gases and has very low drift. Bleaching is not an issue because low energy red light excites the sensor spot and emission is NIR.

Special features

  • High-accuracy measurements of oxygen in gas or water (DO)
  • Low drift
  • Long lifetime
  • Fast response
  • Digital output of all major oxygen units

Technical Data Sheet


Legionnaires’ Risks and Reopening Closed Businesses

Legionnaires’ Risks and Reopening Closed Businesses

Leaving the water systems in buildings unused for some time could be fatal if not properly treated upon return. It increases the risk of legionella bacterium, which can be life threatening.

If you are managing a premises with a water system, you have a legal responsibility to identify and manage any risk of legionnaires’. Read on to learn more about the bacteria and to find out what you should do if you are reopening your business after a period of closure.

Legal responsibilities and assessing the risks

If you are the employer or person in control of premises, you must organise a risk assessment from exposure to legionella. The revised Approved Code of Practice (ACOP) Legionnaires’ disease: Control of Legionella Bacteria in water systems (L8) issued by the Government’s Health and Safety Executive (HSE) significantly extends the scope of its guidance on control of legionella bacteria in water. The code applies to all hot and cold water systems in the workplace regardless of their capacity, i.e. the lower limit of 300 litres previously used to exclude domestic systems, no longer applies. Whilst domestic systems may represent a risk, the code only applies to a risk arising from a work activity. This means that all employers, who manage premises with hot/cold water systems and/or wet cooling systems, have a legal responsibility to identify any risk of contamination and to prevent or control it. These records have to be kept for a minimum of five years.

What is legionnaires’ disease?

Legionnaires’ disease is a potentially fatal form of pneumonia. The cause of the disease is a bacterium called legionella pneumophila.

How is it caught?

Legionnaires’ disease is caught by inhaling small droplets of water suspended in the air which contain the legionella bacterium, e.g. spray from showers and taps.

What are the sources of legionella bacterium?

The legionella bacterium is found mainly in stagnant water, e.g. ponds and rivers or buildings containing cooling tower, evaporation condensers, air conditioning and industrial cooling systems, humidifiers, spa baths and hot and cold water systems.

What areas are the most vulnerable?

A wide range of workplaces, but particularly residential accommodation managed privately or by organisations, e.g. local authorities, universities, hospitals, nursing and care homes, housing associations, charities, hostels, private landlords, managing agents, hoteliers and holiday accommodation providers, including guest houses.

Who is most at risk?

People most at risk are people over 45, smokers and heavy drinkers, diabetics and people who are already ill, particularly with chronic diseases or whose immune system is impaired.

How can using a thermometer help control legionella in water?

Incorrect water temperature is a key risk factor for legionella growth. The legionella bacteria multiply in water at temperatures between 20 to 45 °C. A typical method of control is to store hot water above 60 °C and distribute it at above 50 °C (care must be taken to prevent scalding). Cold water should be kept below 20 °C.

What action should be taken when reopening a business that has been closed for some time? 

The HSE guide to legionnaires’ disease states that:

‘Where a building, part of a building or a water system is taken out of use (sometimes referred to as mothballing), it should be managed so that microbial growth, including legionella in the water, is appropriately controlled.

All mothballing procedures are a compromise between adequate control of microbial growth, the use of water for flushing (while avoiding waste) and degradation of the system by any disinfectant added. Where disinfectants are used, these should leave the system fit for its intended purpose.

The systems should be recommissioned as though they were new (ie thoroughly flushed, cleaned and disinfected) before returned to use.’


RAS takes the heat off smolt producer

Changing over to a recirculating aquaculture system (RAS) brought a bonus for Norwegian salmon farmer Bremnes Seashore during the recent hot, dry weather.While some flow-through hatcheries were practically out of freshwater, the much smaller water requirements of a RAS meant the company never sweated over its supply in the sunshine.

Øyvind Haraldseid: “It feels good not to consume that much fresh water.”

“With the old plant with no RAS and 150 tonnes of production, we would have had to take drastic measures, otherwise there would have been little freshwater left,” said Øyvind Haraldseid, in charge of the plant at Trovåg, north of Bergen. “Instead, we now produce several times more biomass and use less water than ever.”

Freshwater basin

A survey of the freshwater basin used by the hatchery recently showed that the level had dropped by just one metre of a total of 2.6 metres available, despite an extremely dry summer.

“It feels good not to consume that much fresh water, water is a limited resource. RAS is the future of fish farming, it also has other benefits,” says Haraldseid.

The first of a planned four RAS halls has been in operation for two years. The second hall has been in operation for half a year, and the third and fourth halls are under construction.

“With the RAS, we can keep higher temperatures in the plant in winter. Salmon on land are also not bothered by parasites. We plan to keep the fish until they are half a kilo,” said Haraldseid.

3,500 tonnes of smolts 

Bremnes Seashore plans to gradually increase production to approximately 3,500 tonnes of biomass, which is expected to occur in about two to three years.

“On normal flow-through, it would be impossible to produce these quantities on land, at least here at Trovåg,” said Haraldseid. “The RAS consumes little water per kilo of fish;  we have already reduced it by 95% and it will go further down. In combination with the sea water we pump in from 75 metres deep we can let the salmon grow on. In the future I reckon the fish will spend one year at sea, and perhaps even less,” said Haraldseid.

In the long run, it is estimated the plant will produce eight generations per year.

By expanding its RAS and the size of its smolts, Bremnes Seashore will be able to increase production at its sea sites because fish that go in at 500 grams will reach harvest weight sooner. 

Bremnes Seashore is still building its RAS facility at Trovåg, north of Rogaland. The first RAS hall has been in operation for two years, and the second for six months. The third and fourth halls are now being constructed to the left of the existing buildings.

25 times more biomass

Until two years ago, the company had permission to produce 10 million smolts and 10 mill fry per year, limited to 2,850 tonnes, at Trovåg, but has since been given permission for 6,000 tonnes per year at the site if it wants to expand that much.

“In all we expect to increase the biomass on land by a factor of 25. This will use less than half of the water we now have available,” said Haraldseid.

The RAS plants are built as separate units. Hatchery and start feeding are also closed systems. All the equipment is supplied by Sterner, which has also delivered sludge treatment facilities, and has now developed a modular RAS after producing a steady supply of RAS for different customers.

A RAS in six months

“Customers see time as money, we now deliver a module in six months,” said Kim David Lid at Sterner. “If you already have a plant, we prefer to look at it before we get started, as a module is not always the best choice.” He said the firm’s customers also have preference, with some wanting to use ozone while others don’t.

“RAS is not rocket science, but never easy,” said Lid. “Some like to build it on their own. It may work if you have experience and expertise in hydraulics, water treatment and biocultures. Working with a fixed concept like the RAS modules has provided us new knowledge, and in a few weeks we’ll deliver our seventh RAS module. The modules are readily designed in different sizes.”

He said the most common mistake is incorrectly calculating the hydraulics, as large amounts of water and large-dimension pipes are needed.

“A Coke bottle looks nice on the table, but if you turn it upside down you will see that it is not designed for quick emptying. These are the things that must work in hydraulics,” said Lid.

RAS-module as delivered by Sterner

Fish Sludge for Fertilizer

Picture: Osland Settefisk

Osland Settefisk invests NOK 12 million in drying facilities for fish sludge in connection with the expansion of the smolt plant. The end product will have high nutritional value and will be used in pelleted fertilizers.

Osland Settefisk at Sørebø in Sogn is one of the country’s oldest fish farming businesses. Established in 1963 and locally owned by the third generation Osland, it has clear ambitions for sustainable operations. In connection with the expansion of the setfish plant, full recovery of the cleaning sludge is planned. The end product, dried granules will go to fertilizer production.

RAS plant
The plant at Sørebø was early in the process of switching to reuse of water (RAS) and collection of effluent sludge. The sludge contains about 90 percent water, and has so far been transported to a sewage sludge treatment. Some have also been delivered to agriculture, after curing with lime.

In order to be able to supply a more robust smolt, the facility is now being further expanded, from an annual production of 250 tonnes to 1,000 tonnes, within a five million smolt license. This is done with RAS technology, where the investment come to NOK 120 million, with full production in the plant in two years.

– A larger smolt provides a better starting point for growth in the sea and less loss of fish, says Kjetil Rørtveit, operations manager at the plant.

More sludge
The expansion will lead to an increase in the amount of sludge, and after careful considerations it has been decided to invest in a plant for drying this sludge into granules.

– Instead of moving large amounts of thin sludge with about 90 percent water, we dry it to over 90 percent dry matter, and then deliver it for agricultural purposes. In line with a circular mindset, we thus treat the sludge as a resource, says Rørtveit.

The thin  sludge is collected during filtration of the waste water from the RAS plant, thickened and dried at low temperature. Thus, the nitrogen that would otherwise evaporate is not lost, and the granulate receives the greatest possible benefit as fertilizer. The fact that it is dry makes it easy to pellet for so-called “smart fertilizers”.

In total, it is estimated that approximately 100 tonnes of dried sludge will be produced annually when the plant is fully operational. Sterner will supply sludge treatment and drying plants, and the plant will be operational in February next year.

– Obviously it is a significant investment, but we choose to see this as part of the whole, we want to operate sustainably and environmentally friendly, then there is no other way to go. Instead of using large amounts of diesel to carry the gross sludge as waste, we choose to use some electrical energy, reduce the volume to a tenth and make it usable. The sludge has a high nutritional value, so we think that this is future-oriented, says Rørtveit.

Operating expenses
Sterner has ensured that the dried granules are retrieved free of charge for Osland Settefisk and that both transport and further use are in accordance with current requirements. Energy costs including cooling will amount to approximately NOK 300,000 per year. Sterner will be responsible for the costs of polymer, large bags and spare parts.

– We chose to go for the simplest solution in the market, where high ease of use and low energy costs have been crucial to the choice. With this solution, operating costs are kept as low as possible. We have good experiences with Sterner from the past, says Rørtveit.

The drying plant will be operational in the spring of 2020, and the investment in the plant will amount to approximately NOK 12 million. The granulate is scheduled to be delivered to Grønn Gjødsel at Rakkestad.