I wouldn't adjust the pH until I've added everything else to the water that I plan to add.
You might see a magnesium deficiency. If so, add some magnesium. You might see a calcium deficiency. If so, add some calcium. I'd guess that the former would be more likely than the latter when using tap water, but I don't know how much calcium is in your water, whether or not it is in a form that is easily available to your plants, or whether you're using the regular Micro or the hard water variety.
I haven't looked at General Hydroponics' website since Scotts Miracle-Gro's "Hawthorne Group" shell company bought GH, but, if memory serves, the hard water Micro was recommended if using tap water and that water has a total dissolved solids content of 200 PPM or higher.
And it's been
years since I've bothered reading about Lucas Formula, but I was thinking that it was intended to be used with distilled or reverse osmosis water. Which doesn't mean it cannot be used with tap water, but I'd probably go with the hard water Micro if I was going to do it (and assuming my water's calcium content was high - which it is).
I also vaguely remember something about two different dosage recommendations being mentioned with Lucas Formula, and some people getting confused and thinking that one was for the vegetative phase and one for flowering when, in actuality, one was for decent light intensity and the other for less intense lighting. I mention this because... I don't know what your "LEDs lighting (900x2)" would be considered, in terms of strong or weak, across a 16 square foot area. If that's two panels, they actually consume ~400 watts or more (each) of electricity, and you are able to evenly distribute the light they produce onto your plants instead of having dim areas and/or overly bright areas on two opposing walls of your tent... then I'd probably be using the original recommendation, which was intended for HID lighting. If that "900" has no basis in reality, and is just marketing speak for "buy my light, newbies," lol, and your panels are only consuming 300 or less watts each, then I'd probably go with the lower-intensity light feeding recommendation. But that's just a guess.
Lots of factors influence a plant's nutritional requirements; amount of light, temperature, CO₂ level, strain, phenotype, and even the individual plant. Therefore, there really is no "one size fits all" nutrient or feeding schedule, regardless of what some people think. Cannabis is a remarkably resilient plant, so most general feeding recommendations will
work - but you would be well-advised to learn how to "read" your plants, and feed each according to its specific needs; there are numerous pictorials here on the forum and available via the Internet through web searches that would be of great help in this. Look for information about deficiencies and toxicities. There may be something linked from our
How to Grow "Marijuana" Everything You Need to Know mega-FAQ. Even if there isn't, there is more cannabis-growing information available there than in many books.
Some folks add a calcium + magnesium product semi-regularly when using the "Lucas Formula." I don't know if that's warranted in all cases.
If you need one, but not the other - or are concerned about maintaining the important (IMHO) Ca:Mg
ratio instead of just adding a bunch of both - Epsom Salt contains magnesium sulfate (or, technically, the heptahydrate sulfate mineral epsomite (MgSO₄·7H₂O)), and calcium nitrate contains calcium. There are other sources, of course; those are just the most readily available and cheapest in my neck of the woods.
Silica is useful to plants, but (AfaIK) most folks taper off on it as flowering progresses. It's not needed in high doses, anyway, IMHO, so if you add some... I'd "go light." Next time, start earlier, lol.
I'm just rambling. My advice is guaranteed to be worth at least half of what you paid for it
. . . .