By not following specific dosing guidelines the performance of hydroponic nutrients is reduced. Growers must take particular note of these guidelines when using multi-part nutrients (e.g. 2-parts and 3-parts) as these are more complex. Therefore if ease-of-use is desirable then a well balanced 1-part should be used.

The following 3 guidelines apply to multi-part nutrients:

1.  Do not combine concentrated nutrients in too little water:  With 2 and 3-part nutrients, the “parts” are kept separate for good reason – mix these together in concentrated form (or in too little water) and you will see why (Fig 3.1). A white precipitate will form and, depending on the formulation, can happen well within a minute or so. Try this for yourself – mix an equal volume of each part in a glass, undiluted. The majority of the precipitate is typically calcium sulphate. Now, add excess water and see if it will dissolve. The longer you delay dilution, the more difficult (or impossible) dissolution becomes. Along with poor pH control, this is a cause of the white precipitate in nutrient tanks (Fig 3.6b). Therefore to prevent this, always add the majority of water before combining nutrients. Additionally, always stir well before each subsequent part is added.

Note that the source of white precipitate above the water line, on the surface of media and equipment (e.g. clay pebbles) is salt deposition from evaporation. Notably, the amount of precipitation from this source is greater at higher (EC) nutrient concentration.

2.  The part containing the phosphate should be added first: The addition sequence of each nutrient ‘part’ can affect nutrient stability, particularly if the water has high alkalinity. “Alkalinity” (bicarbonate & carbonate) is that component of natural waters that causes high pH. Adding the nutrient dose to high alkalinity water can decrease the stability of several nutrient species (including calcium, sulphate, iron, copper, manganese, zinc). Therefore, instead of pre-adjusting the pH of make-up water (often a very difficult task) it is preferable to first add that ‘part’ of the nutrient that lowers pH the most. This is usually the ‘part’ that contains the phosphate. In 2-part nutrients this is usually part ‘B’. Note that the ‘part’ without any phosphate will have relatively little impact on pH. Secondly, it usually contains the iron which is highly unstable at pH levels much above ~6.5. Note, in 3-part nutrients the phosphate is sometimes dispersed across 2 bottles. Therefore, determine which contains the highest concentration of phosphate, and add that first.

3.  Add equal amounts of each part: Avoid “roughly measuring” out the nutrient dose. An excess of one nutrient species does not compensate for deficiencies in another. In the case of a 2-part, ‘under’ dosing part ‘B’ for example, could cause a deficiency in over half the nutrients required (i.e. P, K, S and all of the trace elements excluding iron). This problem is compounded with 2 & 3-parts because the dose volumes for each part will be roughly one-half to one-third (respectively) of what it would otherwise be if using a 1-part. Therefore, without appropriate measuring equipment, when small tank volumes are being used the dosing error can be significant.

To some growers, the additional complexity of two and three-part formulations is an interesting challenge. To others, who want to make their lives a little simpler, the idea of dosing using multiple parts isn’t so appealing. Certainly, using a high quality one-part formula (Graph 3.1) readily ensures an optimal balance of nutrients and, as a result, one-part nutrient products are increasing in appeal among growers.
 

Whatever type of nutrient you prefer, you should always follow the following dosing guidelines:

+  Thoroughly stir the nutrient: Thoroughly stir the nutrient: Always stir immediately after the addition of nutrient, additives or top-up water. Doing so will eliminate high zonal concentrations of the less soluble nutrient species. Further, it removes zones of extreme pH (either high or low), thereby preventing the destabilization of nutrients that are unstable outside of the optimum pH window of 5.0-6.5 (Fig 1.11).

+  Be diligent with pH? This is probably the most crucial area of nutrient management.  For detailed information on this see section on “adjusting nutrient pH in hydroponics”.

+  Beware of high pH additives: Note that essentially all additives will affect nutrient pH at least slightly. The best technique to adopt with those that elevate pH significantly (e.g. silica, PK additives) is to add them to the water and adjust the pH down to ~6 prior to adding the nutrient.

The less preferred but common alternative is to pre dilute the additive in a separate volume of raw water prior to adding to the nutrient solution, then quickly lower the pH to below 6.5 once this solution is added. Note, a white cloudy precipitate (calcium sulphate) may form when the pre diluted additive initially merges with the nutrient solution (Fig 3.6a). However, because the initial particle size of the precipitate is small, it will usually re-dissolve if the pH is immediately re-adjusted.