| Many of the fertilizers available in the marketplace are in
powder form, as they can be formulated to be more concentrated and can be
shipped less-expensively than liquids. While that does make them more
economical to purchase, there are some issues with them that can complicate
life for the hobbyist. One of those problems may be a lack of homogeneity or
uniformity in the powder. A fertilizer manufacturer typically makes many different formulations utilizing a variety of minerals. They therefore keep stocks of those mineral raw materials and blend them in specific proportions to create different formulas. Some of those raw materials are powders, some are chunks, and some are "prills" - little spherical particles - and when you mix them, it's not a truly uniform blend. To a large-scale user who might consume entire bags, it's not a problem, but for those of us dipping a spoonful out of the package, it may result in slight differences in the final chemistry each time we mix up a batch of nutrient solution. Then there's the measuring of the powder itself. We hear mixing recommendations of "teaspoons per gallon" or "milliliters per liter", but those are volumetric measurements while the contents of the fertilizer package are expressed in weight percentages on the label. Even if we've graduated to using parts-per-million controls - a mass-to-mass measurement - we're still stuck, because we don't know the bulk density (weight per volume) of the formula (unless it's provided by the manufacturer), which would allow us to do a simple mathematical conversion. The fact that the bulk density can vary between formulas further complicates matters. Another problem is that many of the raw materials are extremely hygroscopic - they "suck" moisture right out of the air over time. As there is no practical way for us to know exactly how much water has been absorbed, we can no longer use weight to accurately measure how much to use, and as it affects the bulk density as well, volume measurements are thrown off as well. So what can we do? The answer is really quite simple: make a concentrated solution!
You now have a 25% concentrated solution of your original formula. In other words, if the original powder was a 20-20-20, your solution is one-fourth of that, or 5-5-5. The advantage of this is that it's totally uniform (just be sure to shake well before measuring it). it's not going to absorb more water from the air (keep the container closed to prevent evaporation), and you can now work on a volume-to-volume basis to mix your nutrient solution. Note that some formulas, particularly those containing higher levels of calcium, should be mixed far more dilutely to prevent precipitation. |