Getting the Most From Your Bluelab Pulse Meter: A Complete Calibration Guide

Calibrating the Bluelab Pulse Multimedia EC/MC Meter 

For growers seeking precise control over their growing environment, proper calibration of soil moisture measurement tools is crucial. The Bluelab Pulse Meter is an advanced tool that measures pore water EC and moisture content, but like any precision instrument, it requires proper calibration for accurate readings. Here's everything you need to know about calibrating and using your Pulse Meter effectively.

Why is calibration required?

Different growing mediums have varying moisture retention characteristics. From sandy soils to clay-heavy mixtures, each substrate has its own optimal moisture range. That's why calibrating your Pulse Meter to your specific growing medium is essential for accurate measurements and healthy plants.

Pulse has been developed to accurately measure conductivity and moisture content in different medium types. As you can see from fig1 (above) the optimal moisture level ranges vary for substrates and soil types. Calibrate to your specific soil mix, create different calibrations for each. 

Getting started

To prepare for calibration you will need to select a sample of plants of the similar root zone characteristics and irrigate to maximum water holding capacity (WHC):

1. Select 2–5 pots or field test areas that best reflect the soil type and moisture conditions per calibration name
2. For both potted and open field plants, apply water until the soil is fully
saturated.
3. Let the soil free drain for one hour.

Open Field: Allow the soil in the test area to drain naturally for at least one hour. Adjust this time depending on soil type (clay soils may take longer, while sandy soils may drain faster). Ensure the soil is moist but not waterlogged after draining.

Potted Plants: Allow the pot to sit and drain freely, ensuring that excess water has drained, and the soil is moist but not saturated.

Choosing the Right Base Medium

The Pulse App offers two primary configurations. In the Configure screen within the app choose either:

1. Mixed Media - For general mixed media blends. Measures volumetric moisture content, temperature and pore conductivity of the medium.

2. Mixed Media (Coir) - For mixed media predominantly made of coco coir (50% or more). This corrects for the effect of coco coir. Measures volumetric moisture content, temperature and pore conductivity of the medium.

FAQ's:

When should I calibrate/recalibrate?

Because the maximum WHC of the medium changes with plant age, due to increased roots and medium compaction, the same plant may need to be recalibrated with Pulse to account for the change.

To test if Pulse requires calibration to the medium:

1. Irrigate the container to saturation and leave to freely drain for one hour to reach maximum WHC

2. Test moisture levels with Pulse with the current calibration programmed.

3. If the moisture measurements are between 90% and 100% of the maximum WHC the calibration is still relevant. If the moisture is below 90%, make a new calibration following the same as above.

Clearly name the new calibration including information like the container type or size, the plant type and the age of the plant to differentiate it from the first calibration.

What exactly is the Pulse reading?

The Bluelab pulse measures pore water EC. That means it determines the ability for the water in the soil pores to conduct electricity opposed to bulk EC which measures electrical conductivity of soil, pore water and air. With Pulse, you get the reading of nutrients that are available to your plants right now, not all ions in the soil that may not be in a soluble form.

I calibrated, but even after fully saturating my soil I get less than 100% for moisture.

There are multiple reasons why you might sell less than 100% including not waiting long enough or not fully saturating your soil, choosing the incorrect base media or not measuring the same depth each time you take a measurement.

I take two measurements at the exact same spot and get different readings, why?

As you push the pulse into the soil and taking it out you are disrupting the soil and the capillary action holding water to the soil particles. This in turn affects the EC and moisture reading for that particular spot. We recommend you always take multiple readings around each plant to get an average and compare that to historical readings to determine the next course of action for your plant care.

Is the probe replaceable?

The Pulse probe is not replaceable. Bluelab offers a one year warranty. With proper care, the Bluelab Pulse can last many years more. It is not suitable for use with Rockwool or in extremely rocky soil as that can damage the prongs.

Why do I get different EC measurements with my previous method compared to the Pulse?

Traditional EC measurement methods often involve diluting soil with water, which affects the EC value. Shaking, stirring, and the duration of extraction can also impact the number of conductive ions measured. If you’re familiar with your previous EC testing method, try comparing it with Pulse by testing the same samples. Pulse readings may show slightly lower values than traditional extraction methods.

Is there a minimum moisure level?

Pulse requires at least 5% moisture content for a reliable moisture reading. Below 5% a measurement will be generated but with reduced accuracy.

Pulse also requires above 20% moisture content for any nutrient (EC) measurements. Below this level there is very little water in the medium pores reducing the accuracy of the nutrient (EC) measurement.

By following these guidelines, you'll ensure accurate measurements and make the most of your Bluelab Pulse Meter. For more information and detailed instructions, watch the video here: