I was trying to calculate amounts of nutrient solution components, using widely available and cheap commercial soil fertilizers and "elementary" chemical components when I realized a demand of calculator, which would automate this task to some extent. Majority of nutrient solution calculator software uses either only separate "elementary" substances or commercial hydroponics solutions, but not both at the same time. Though it's quite convenient to use different commercial fertilizers (containing a set of macro and microelements) and simply add missing elements and/or adjust element ratios. Fortunately, i found such a calculator - HydroBuddy by Daniel Fernandez. Available for Windows, Linux, Mac OS and source code (Lazarus). It's free (donationware, worth donating).
It operates any combinations of source substances - "elementary" chemicals, predefined and custom substances, all together. It calculates mass or volume amounts of subsctances based on desired amounts of nutients and solution volume, allowing imprecision if it's not possible to achieve perfect ratios with your source substances, taking water properties in account. It predicts EC, calculates overal cost and more..
There are some obvious minor issues in current version (1.50), e.g. unicode support is not in place yet, so don't use unicode names for components. But it does not affect the practical usage.
So my task was to assemble a solution for growing arugula. Here [Russian only] i found a recipe for growing ether oil-yielding plants, which should be good for arugula:
Most of these are present in commercial soil fertilizers (for example "Rastvorin", local Russian brand - N/P/K: 18/6/18, Zn, B, Mn, Cu, Mo), but, as many soil fertilizers, there's no calcium at all. There's also no iron or magnesium. Widely available source or calcium (with nitrogen on top) - Calcium Nitrate. Iron - Iron Sulphate or Iron Chelate complex. Magnesium - Mg Sulphate (used in medicine), Mg Carbonate (used in sports) or Potassium/Magnesium sulphates mix used as fertilizer. There are also other widely available soil fertilizers with different ratios and sets of elements, which can be used together, but calculation gets even more complex in this case. With HydroBuddy it's as simple as this:
Specify amounts (in ppm) of all the nutrients, save them for future use. Specify amount of solution we need - i only need 16 litres at once.
Add custom substance, e.g. "Rastvorin" and specify its contents:
I also added two more custom substances - "Mix NPK" (N/P/K in 13/19/19 ratio, good to have for low Nitrogen solutions) and "Kalimagnezia" Potassium/Magnesium mix (28/9 ratio).
Chose components to use. Calculator will complain if source substances has no source for any necessary nutrient. It will warn you if any of the specified substances are considered useless. For example, i do have some Ammonium Nitrate, but it's useless in this case, as nitrogen is already in excess thanks to other substances i specified.
Here's te result.
That's almost perfect. I ignore Molybdenum for now, as i have no separate source substance yet to fix it..
By adding a bit of Potassium Nitrate, absolutely perefct match to original recipe can be achieved:
A pinch of Molybdenum is all i need now :) But Arugula looks good enough with this solution already.