This is a frequent question on this forum, we're always glad to help. You're working with hydroponics, which is always interesting for its peculiar problems, and for the simplicity of working with a soil-less system, because that removes some variables.
Hydroponics is interesting. I use modular Kratky and modular Dutch bucket systems, so for the most part they are “plug and play.”
I can break the system down in portions when harvesting and not effect other portions, which is very convenient.
Hydroponics is nice but lacks the “feel” of a garden, it is more sterile which is fine with me.
As you said it cuts down on variables, making diagnosing issues a lot easier.
No. That's false. At least as you've written it here. You may want to qualify the statement more, to talk more about what you really mean. But if you have calcium nitrite, or potassium sulfate, or urea as other examples, and you make a stock solution, it will stay the concentration you made it, indefinitely. I mean that as its defined -- forever, but without a defined point at which it loses potency. You have to add qualifiers that are sourced for us to help you with all possible problems.
Ok, let me explain a bit better.
The fertilizer is a three part formula, the base fertilizer, calcium nitrate, and magnesium sulfate.
I have spoken to my fertilizer supplier, they have suggested to not leave a stock solution on the shelf for more than a few months, but they didn’t explain why.
The variables here could be many things, from the fertilizer solution growing algae from ambient light to the filler they are using going off and putrefying (42% of the fertilizer is filler, as is the case with most powdered fertilizers). I suspect the filler to be a form of cellulose.
I have mixed stock solutions before and left them for periods of 2 months and upon opening there is this distinct ammonia-like, chlorine smell (the smell is difficult to describe, I have nothing definite to compare it to) leading me to believe that the fertilizer is off gassing something.
Also I have run tests where I have “pre-mixed” the dry components, which have ended in failure. The fertilizer first turns to slush, then re-crystallizes into this lump. Also when mixing pre-mixed fertilizer into a stock solution, there is always sediment in the mixing container, which looks to be calcium on visual inspection.
When opening the containers of the pre-mixed fertilizer tests there was a very strong smell of this same ammonia-chlorine smell.
I did the test a few times to make sure the same results would occur and have not repeated it since.
Also, sometimes in the summer when I open the container I keep the dry calcium nitrate prills in (gamma seal on 5 gallon bucket), there is this same ammonia-chlorine smell, which by deduction leads me to believe the scent I am smelling in both the stock solution and the pre-mix are from the nitrogen.
The smell must mean something is off gassing, so I assumed it
Also I remember reading this somewhere, but I don’t remember where. I know that is very helpful!!!
My goal is to be able to mix something around a gallon or so of a “concentrated” stock solution that I can draw from over time.
The fertilizer I am using is a commercial fertilizer and it really isn’t suited to mixing in small batches.
Thank you again for all of your help, Ken