Grow Hack: Measure Nutrient Solution Accurately

Don’t ever let improperly measured nutrient solutions bring you down again; all it takes is good practice and the right equipment. Check out some of these tips on measuring fertilizer solutions to avoid the frustration and imprecision of taking multiple measurements for one solution.

When it comes to measuring fertilizer for soil or hydro, many novices will be tempted to simply use an eyedropper or one of those plastic, 3 mL pipettes that sometimes come with fertilizer solutions. Both eyedroppers and small pipettes only deliver one to three milliliters at a time, forcing you to make multiple measurements. Each measurement you make has a small amount of error associated with it, and over multiple takes this error compounds. Measure liquid fertilizer in as little steps as possible to avoid large uncertainties in your measurement.

How much will the uncertainty compound with multiple pipette measurements? Let’s say you need to measure 7.5 mL of nutrients to the reservoir and you have a pipette that can deliver a maximum of 3 mL. You would have to transfer three milliliters twice, then 1.5 milliliters once. Plastic pipettes aren’t designed to be incredibly precise, and each measurement comes with a 10 percent inherent, unavoidable uncertainty. This 10 percent propagates, and the final volume you deliver could be anywhere between 7.05 mL and 7.95 mL!  

For most nutrients, the best tools for the job are either a graduated cylinder or a syringe. These receptacles will allow you to measure liquid consistently and easily. The graduated cylinder should always be plastic; the wrong glass can be contaminated with toxic mineral impurities.

Read the feeding schedule of your nutrient before you start. The container you use to measure should. If the chart calls for quantitates of nutrients less than 10 mL, buy a container that holds 10 mL. If it calls for amounts of fertilizer higher than 10 mL, get one that can hold up to 25 mL.

To use a 10 mL graduated cylinder, use small pipette to fill it the bottom of the meniscus is level with the desired reading when looking at it straight on. What is a meniscus? Notice how water “clings” to the sides of a container; when the water is in a narrow tube, the surface of the liquid forms an upside-down dome, the meniscus. Align the lowest point on the meniscus to the line that measures the volume you want. Pour into a small cup and rinse with clean water to remove any remaining drops.

Syringes measure volume only by difference. For example, in order to measure 3.5 mL, pull out roughly 5 mL, flip the syringe facing up and push out the bubble so only liquid remains in the syringe, adjust the volume to exactly 4.5 mL, and squirt the contents of the syringe into a small cup with reservoir water until the syringe reads 1 mL, for a total delivery of 3.5 mL (4.5 – 3.5 = 1). Syringes can be very accurate, but always measure by difference only and make sure to get rid of the bubble so all you measure is liquid.

Whatever you decide to use, plan out every step before starting and be as methodical as possible. After you measure something, don’t pour it directly into the reservoir or watering jug, always pour it into a small cup first to prevent any mistakes.

Photo Credit: VortexFarmacy


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