11:30 – I was making up nitrogen-free fertilizer stock solutions for biology kits yesterday when it struck me again as so odd that I’m using reagent-grade chemicals to make up fertilizer solutions.
Each of the solutions contains macro- and/or micro-nutrients. We have to supply them as three separate solutions because if you try combining them in the concentrations needed for stock solutions, you get a nasty precipitate.
So I made up 15 liters of Fertilizer A, enough for 120 kits at 125 mL/kit. Fertilizer A is basically just a concentrated solution of monopotassium dihydrogen phosphate and dipotassium monohydrogen phosphate. (You use a specific mix of the two chemicals to maintain the proper pH.) Fertilizer A supplies potassium and phosphorus, both of which are macro-nutrients (The “PK” in “NPK”). That solution, as expected, turned out clear and water-white.
I went on to make up 2 liters of Fertilizer C, which provides calcium, cobalt, and boron ions. Again, that solution turned out clear and water-white.
Ah, but then I went on to make up 4 liters of Fertilizer B, again enough for about 120 kits at 30 mL per bottle, and provides magnesium, iron, copper, manganese, molybdenum, and zinc ions. What a mess. There’s not a precipitate per se, but the solution is a cloudy brown. Cloudy enough that I don’t want to run it through my dispenser pump, which is a precision instrument. So I guess I’ll hand-fill 120 30 mL bottles. Better that than buy a new dispenser pump.