I am a bit confused by part of this. it seems you are trying to take every fertilizer recommendation out there and turn them into one "unified theory"---good luck!
There are two calculators on the page. One takes the fertilizer formula and the amount you're adding to a gallon to tell you the TDS of the macro elements in the final solution. The other is used to take the nitrogen concentration of the fertilizer you have, and using your targeted final concentration, tell you how much of that to mix up to get it.
If you are starting with a 4.24%N concentrate, and want 125 ppm N in your final concentration, the calculator at the bottom of the page recommends roughly 2.25 teaspoons per gallon.
Think of the concentration as a "calorie count" for the "meal" you give your plants. Think of the frequency of feeding as the meals provided.
With no claim of what is "right", I like to feed the 125 ppm N solution to S/H plants at every watering. That does not mean the plant takes it all up, it just means that's the supply. By replenishing it frequently, I am more-or-less assured of a "constant" nutrient supply for the plants. If I only fed once a month, I'd have to multiply that concentration to provide that same "supply", but there is a limit to how much a plant can take, so a little, frequently seems to be a better approach that an infrequent overdosing.
Concerning the Dyna-Go recommendation, the range of addition jives totally with the frequency-of-feeding example I just gave. What doesn't jive is the concentration recommendation.
At 7% N, if you want 125 ppm N in the final solution, you will - indeed - need to mix up the 1.43 tsp/gallon. That is cold, hard science, nothing else.
The 1/4 - to 1 tsp/gall rates are 23 ppm N to 92 ppm concentrations. Again, a simple calculation that cannot be debated. If you want to use the 1/4 teaspoon concentration and provide the same MASS of nutrition as the 125 ppm level, you'd have to feed 5 times as often.
The bottom line is this:
- Plants need a certain mass of nutrition to thrive.
- Mass provided is equal to concentration x frequency.
- Nobody knows exactly what mass a particular orchid needs, so it makes sense to keep an adequate supply available, and let the plant decide what it needs.
- One needs to apply some level of reason to that - watering once a month is like starving and binging; many small "meals" is more reasonable (and won't poison the plant with too high of a concentration of mineral salts).
- What constitutes that appropriate "mass" is - to a great deal - a matter of opinion. Dave Neal (owner of Dyna-Gro) is a believer in very little nutrition, as he feels it fosters new root growth to search for more food (we have discussed that extensively). My opinion after almost 40 years of growing is that environment determines the root growth, and that food should be sufficient to foster the health of the plant.
So basically, it's up to you how much you want to feed, and how you want to do it, but infrequent, highly-concentrated "meals" should be avoided, just as they should be for you and me.
And, since I don't exhibit in shows or do OAS judging, I don't need to worry that the batch I water with on May 30th is not exactly the same as the batch I mixed on April 20th. I also use it fast enough that I don't need to worry about it absorbing moisture and melting.
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