I am growing “soil-less” in Pro-Mix HP without amendments under 3500k LEDs and using RO/DI water.
Like @Bogleg and for the same economic reasons, I am basing my nutrient schedule on Jack’s Nutrients, with some differences:
I am using the 3,2,1 system, but as a ratio, not by weight.
Base Formula:
Jack’s Nutrients 5-12-26 (Part A) - 3.6 g/gal (add first)
Jack’s Nutrients 15-0-0 (Part B) - 2.4 g/gal (add last)
Epsom Salts (Magnesium Sulfate) - 1.2 g/gal (add second)
Ratio by weight: 3:2:1 NPK ratio: Approx. 3:1:4
Tribus Original: While not “required” and the stuff is expensive, I plan to supplement regularly with Tribus Original. It is a bacterial inoculant with incredibly high numbers of certain targeted bacillus strains that according to my primary source encourages massive and healthy root growth. I want that!
Supplemental “GG “Boost” Formula” (OPTIONAL): During the first two weeks of flowering, I plan to switch to this:
Jack’s Nutrients 5-12-26 (Part A) - 2.0 g/gal
Jack’s Nutrients 15-0-0 (Part B) - 2.7 g/gal (can drop this down to 2 or anywhere in between as required)
Epsom Salts (Magnesium Sulfate) - 2.0 g/gal
MKP (Mono Potassium Phosphate) - 1.2 g/gal
Note: There is no clear evidence that this “Lucas”-like “boost” formula provides any significant benefit over the base Jack’s 3/2/1. So this is an optional deal. You can successfully go from seed/clone to harvest with JUST the Jack’s 3/2/1.
NO CALMAG!!! You do not need it. You can control Calcium and Magnesium levels independently and BETTER by varying the basic component ratios.
Note: I will not be using the Jack’s cloning product or any other product for clones, seed starts, seedlings, et al. I will be using Jack’s “3/2/1” from seed drop to harvest. I will simply control the concentration in solution (lowest for pre-soaked starter plugs for seeds, a little higher for starts, little more for seedlings, building to full strength for veg and flower.
FULL STRENGTH on the Jack’s (3.6/2.4/1.2 g/gal) is about 730 ppm (true), but you have to normalize the relative ppm to YOUR meter and meter scaling/conversion. (GG Boost is a little higher at about 755). IF I decide to push the ppm level at any time, I can just up the concentration, BUT MAINTAIN THE SAME RATIOS.
MycoMadness: This is an endo-only myco + bacilli in powder form. I plan to use it dry to dust root balls and line depressions at each transplant to encourage mycorrhizal fuction and favorable bacterial action. Totally optional, and there is no hard evidence that it will work in soil-less, especially at the pH ranges and P concentrations we use. I’m doing it anyway. 
Silica: Like @Bogleg, I plan to add a Silica supplement. SiO2 will not work directly, because it is insoluble in water and thus unavailable to plants. Plants require Silicic Acid in order to take up Silica freely. I am looking at Potassium Silicate, K2SiO3 (dry) as a potential source of making a solution locally to yield silicic acid for plant uptake, but this is, strictly speaking an “optional” step.
I choose to pursue it in hopes of making plants stronger structurally and boosting resistance to various potential disease vectors. NOTE: The solution is quite alkaline, and care must be taken to add in the correct order and manage the pH. I will likely use this as an opportunity supplement when I want to push the pH up toward the higher range to insure higher availability of nutrients that require pH above the “standard” 5.8 that is commonly targeted.
Magnesium, Calcium, LEDs, and pH
I have some thoughts on the whole Calcium and Magnesium deficiency, et al. as they relate to pH and to a lesser extent LED lighting.
In soil-less and hydro, I see LOTS of posts about farmers fighting to get their plants enough magnesium and calcium, especially under LEDs. I also see a significant number of cases of other nutrient deficiencies in the micro list.
Additionally, I see many recommendations about pH ranges that are “optimal” sometimes even targeting a specific number vs. a range. Then, I started looking at various nutrient availability charts vs. pH. As a “newbie” to this sort of intense management and cannabis, it struck me that the pH values that are often recommended are “on the edge” of nutrient cut for some of the nutrients… specifically magnesium and calcium.
I need to do some more research here, because even confining the search to hydro or soil-less nutrient availability charts reveals many inconsistencies in pH levels, taper, and cutoff points, but the trends are consistent.
Bottom Line: I THINK we MAY be OVER-managing pH. That is to say, I think many of our nutrient deficiencies are self-inflicted by maintaining the pH in TOO NARROW of a range ALL the time. It is my hypothesis that for each medium type, there is a pH RANGE that the farmer needs to NOT ONLY stay WITHIN, but it is equally necessary to “survey” that range or purposely PUSH the environment up and down the range in order to make all of the various macro and micro nutrients available to the plant as required.
I do not know yet how to test or prove this. Nor do I yet have a firm handle on a procedure or timing schedule for where the pH needs to be when, for how long, et al. It’s just a theory, but it makes sense to me.
CREDITS: I didn’t come up with ANY of this. I merely read and watched videos. Here is where I got most of my information:
Greengenes Garden (Youtube)
All of his videos are good, but I focused on the ones dealing with Jack’s (as supplemented).
OK… so this got way more involved than I intended… 
