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7 Tips to Fight Fouling and Extend Sonde Deployment


Learn how to protect your water quality monitoring sondes from Biofouling, extend deployment periods and increase the quality of your data.

To better understand an environment, to make better informed decisions towards water quality management, and get the full scope of what is happening in a river, a lake, a stream, etc, it is critical to obtain high resolution data.

However, that is not enough, if data is not being constantly collected. Ideally, 24/7, 365 days a year. Which can be hard to maintain via handheld instrumentation. That’s why sondes are critical to building a global, high resolution water quality data set.

Water quality monitoring sondes can autonomously record water data in-situ for weeks or months at a time, regardless of weather conditions.

This equipment keeps recording important parameters on the health of a waterbody, until they are pulled from the water or run out of power.

After overcoming some battery-life hurdles and limitations, the focus of sonde manufacturers turned to the quality of the data being collected. Depending on the environment, the deployed sensors could be coated in sediment, biofilms, or even barnacles, within just one day! Which skews the data, making it nearly worthless.

In addition to that, trying to maintain or even service the sondes in harsh aquatic conditions, or sometimes in remote locations, was proving to be a logistics nightmare, quite time consuming and resource intensive.

The conclusion was clear: The cost per data point is extremely expensive when your sonde can’t keep its sensors clean of debris. Sensor fouling or biofouling, like algae, silt, and microorganisms, is the true enemy of high-resolution data sets.


So how can you fight biofouling and collect the highest quality data over the course of a long-term water quality sonde deployment?


YSI experts give you seven tips that will not only do that but also help you to reduce the frequency at which your team must travel to field sites to clean and maintain water quality monitoring sondes and sensors.

Even though some of the tips can imply you require certain probes or accessories that can be more costly, they’ll pay for themselves in no time by saving you time, money and resources.

How? By extending maintenance intervals on your equipment from once a week to once a month, there’s no telling on how much you could be saving, even if only one trip is avoided – specially to remote locations.

Continue reading to learn the experts' tips or watch the YSI webinar.


Tip #1: Copper-Based Anti-Fouling Paint

If you’ve been using sondes for a while you may be familiar with copper-based anti-fouling paint. This paint is widely used in the marine industry to cover hulls of ships and effectively prevent barnacles and other marine organisms from growing and reducing the ship’s performance. Using this type of paint in a sensor, can help achieve the same effect.


The copper components in the paint, like copper oxide and a variety of aromatic hydrocarbons, make it very important to take all required safety precautions recommended by the paint manufacturer when applying the anti-fouling paint (like using protection gear).

Petit Paint’s “Trinidad SR”, and Interlux “ACT BottomKote” are the two anti-fouling paints with a successful proven record with YSI sensors. Even though there are no long-term effects to using these paints on the instrumentation, this paint cannot be used in the sonde or sensor connectors.

With this paint, not only will a sonde be able to provide high-quality data for longer periods of time, but also any organisms attached to the sonde are more easily cleaned off.

How to paint the sonde?

Remove each sensor and apply paint separately, along with each part of the sonde including the guard. For maximum effect the paint should be applied in thin coats, allowed to dry and reapplied. Black paint must be used, and some maintenance is required as paint can flake off over time.

A few considerations: Even though applying the paint has had some successful results, the painting process is time consuming and there are increasing concerns over long-term toxic effects.


Tip #2: Copper Components


More than a decade ago, YSI introduced copper components in sondes – like copper guards, wiper blocks, copper tape, mesh screens, copper probes - , as a slightly more efficient, more environmentally-friendly and less time-consuming way to prevent fouling.

In the same way as the copper-based paint, organisms have a hard time attaching to these components, which allows for extended deployment times, without having to do any modifications to the sonde.

A good example of this would be the copper tape, from which you can expect about a month or so of life before it needs to be reapplied. However, you shouldn’t leave it for too long. The tape is easier to remove if it is still somewhat intact. This is easy to apply as well, simply clean your probes and wrap the tape around them so they are completely covered.

Other components like the copper guards, wipers, and probes can last years. Read our blog post "Get Your Sonde Field Ready" to learn more about these components.


Tip #3: Use Mechanical Wipers

The number one accessory to help reduce fouling would be a mechanical wiper or wiping system, that sweeps over the sensing surfaces between measurements.

Before, each optical sensor used to have its own wiper, but newer technology has introduced a robust central wiper, with more torque and stronger bristles, to clean all the sensors at the same time. More thorough and easier to maintain, as there is only one brush to clean.

While this is a great solution to keep sensors debris-free, the rest of the instrument still needs some attention. Accessories like shrinkable plastic sleeves can form a protective layer between your instrument and the environment and make clean-up a lot faster. Be sure to apply a layer of copper tape over these sleeves for harsh aquatic conditions. Copper alloy screens and guards also work well to keep biofouling at bay.

Having just a few of these accessories will save you hours of cleaning, even though in some situations an acid soak and some scrubbing will still be needed.


Tip #4: Keepping Up With New Sensor Technologies


The sondes conductivity sensor is what’s called the Achilles heel of anti-fouling. Most conductivity cells are susceptible to interference from fouling in one way or another.

Even though these sensors have their electrodes well-hidden within the probe (and not accessible to any wiper), sometimes small aquatic life or algae can find their way in and the build-up that can arise from that will interfere with your measurements.

Conductivity sensors are designed with “drive” electrodes to send current through the water towards a receiving electrode. The amount of signal loss between those two electrodes is what is used to calculate the conductance of the water. If the connection, or path, between the conductivity sensor and the receiving electrode is obstructed due to any algae build-up or other debris, the quality of your data will be compromised as it will record an artificial drop in the conductivity reading.

If the conductivity sensor is not regularly checked and cleaned, its poor performance can impact on other paraments. For example, dissolved oxygen, depth and level parameters use conductivity reading to compensate for changes in salinity.

Understanding the impact and importance this has on long-term deployment, YSI released a Wiped Conductivity and Temperature probe for the EXO sonde, specifically made for high fouling, long-term monitoring projects.

The new technology of this probe is simple: it raised the conductivity electrode to the same level as the other sensor faces, allowing the EXO Central Wiper to thoroughly clean the measurement surfaces. This will keep organisms from interfering with your conductivity measurements.


Tip #5: Instrument Maintenance Pays Off

Regular maintenance of your instrument – according to manufacturer’s recommendations – will help increase the life of your product, but also the quality of your work and data.

By sending your instrument back to the manufacturer or a certified reseller to be checked by an expert technician, you can have the peace of mind that he will check items like internal o-rings, internal torque adjustments, and carry out tests, such as power consumption, pressure, and other specification tests of the system, that will keep your instrument working to the high level you require.

There are also things you can do, like cleaning in between deployments. This is imperative to minimise fouling and also to help create a habit of inspecting your unit.

When you do these regular clean ups, you are minimising biofouling by removing biofilms that micro-organisms create and that could affect the surface of your instrument in many problematic ways:


  1. They condition the instrument surface, provide an enzymatic interaction for exchange of nutrients, protection against environmental stress, and increase resistance to biocides
  2. Once formed, they change the instrument surface chemistry which can lead to macro organism growth, like barnacles
  3. They also interrupt ion flow, acting like a diffusion barrier, which can lead to localized corrosion

What do you need to carry out a through clean?

  • Mild dish soap
  • Dish brush
  • Plastic putty knife
  • Clean water, tap water is okay
  • Non-abrasive scouring pad
  • Manufacturer issued CT brush, grease, and syringe
  • White Vinegar or 1 molar HCl

For removing soft fouling, like muds, silts and worms, a mild dish soap, a brush and a good scrubbing will do just fine. After you removed the bulk of fouling, you can then clean each sensor more thoroughly with a scouring pad.

To take care of harder fouling, like barnacles, a short soak in 1 molar hydrochloric acid, typically 10-15 minutes will help to break down the organisms. After that, a brush and scouring pad will work well. Be sure to use appropriate protection gear when dealing with acids, and to rinse well after soak. White vinegar will also work as a replacement for the acid, it might just need to soak for longer.

The next step is to check the cable’s integrity and if the connectors are debris-free. Check the integrity of the seals as well. You can apply the grease to connectors and o-rings to see if you catch any grit that could compromise the seals. Inspect the integrity of the securing items like the bail, carabiners, and chain as well.

An easy one to forget is the level or depth sensor, as it is built into the sonde. The depth port hole is very important to check. It can easily get obstructed with foul as it allows water to flow through the instrument and to the internal depth sensor. Signs of an obstructed depth port are: increases in depth or unexpected measurements when the sonde is on the lab bench.

Fill the small syringe supplied by the manufacturer with clean water. Force the water into the depth port hole and watch the other hole for water exiting. If it doesn’t, then there may be a blockage. If soft fouling is suspected, then try soaking the area in warm soapy water then repeat the clean water cleanings. If hard fouling is suspected, try soaking the area in some white vinegar. Do not try to clean this area with a brush or pipe cleaner. Follow up the vinegar soak with several clean water flushes.

A very important step of your clean up should be your wiper. Checking your brush for splay and your pads for wear and tear is imperative to avoid reducing your wiper’s effectiveness. This is your first line of defense against fouling, so you must keep it in top shape.

Wiper brush/pad replacement is governed by the site, season, and sensor payload. Low fouling sites may get months of life, while other sites may need changing after only weeks of deployment.

Keep in mind that following the manufacturer’s guidelines for maintenance will help to protect your equipment and give you confidence in your data.


Tip #6: Consider Your Deployment Location


All the time and effort you put into preparing your sonde for deployment will be wasted if you place it in a deployment location that has not had any protection or preparation. The pipe or tube where you place your sonde require almost as much protection and maintenance as your sonde.

Things like applying anti-fouling paint to the sonde protecting tube or cleaning the inside of the pipe with a brush and getting it serviced, are a few steps you can take to extend the collection of quality data.

A few other things to think about regarding the deployment site to help prolong your deployment:

  1. When using a solar panel to charge a battery which powers your site, make sure the solar panel is pointing in the right direction and it’s kept clean of branches or leaves, as well as the most common type of fouling which is bird droppings.
  2. Make sure the site you pick is as easily accessible as possible. If you can, choose a site which doesn’t require a lot of logistics to access. This will automatically make it easier to service, which helps to extend the deployment time.


Tip #7: Telemetry Helps Keep an Eye on Your Field Site

Water quality sondes can be connected to data loggers with the ability to wirelessly communicate data to a web portal or online database. This is what we call telemetered data.

You can use this live data to drive the frequency of your maintenance visits to a site. How? Easy! If you regularly review your data, you know by now when certain parameters appear to be impacted by sensor fouling. By giving you access to your sites’ data either via smart phone or pc, you can let the instruments’ inform you of when maintenance may be necessary.

Take advantage of telemetry giving you a live view of your sonde data to help you decide whether or not it’s necessary to spend your time, energy, and resources visiting a site.


How Can I Keep My Sondes Clean of Fouling?

Should you like to know more about how to keep your sondes and sensors in top shape for water quality data collection, please contact our Environmental Sales Specialist and check out the range of water quality monitoring sondes we have available on our website.

You can also read the full article from YSI here.

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