The non-refillable Blue lab Soil pH Probe is used to test the pH levels of soils, substrates or media of cropping, pasture, turf culture, containerized plants, home gardens, orchards, tree farms, greenhouses, propagation culture. Anywhere that the soils" pH requires testing so adjustments to the soils can be made quickly. Yellow leaves, stunted growth, slow growth, are all signs that the plant is not getting the nutrients they need from the soil. This is often caused by "lock up". This is a situation where the plant loses the ability to absorb specific nutrient elements because the pH value of the soil is incorrect. The Blue lab Soil pH Probe is a replacement probe suitable for use with Blue lab handheld products like the Blue lab Combo Meter, Blue lab pH Meter and is the replacement probe for the Blue lab Soil pH Meter. It can also be used to measure the pH of solutions too!.