cannabineer,
Thank you for stopping in and welcome back.
The burn developed after four heavy feedings and a topdressing of Jamaican Bat Guano. There are likely a number of factors involved.
As I understand necrosis, the plant will allow the affected leaves to continue to until they have died and fallen off completely. It will not try to repair them but focus on new growth instead. Resolution of the problem should be exampled by the health of new growth. Is this correct?
In regards to the water; yes, 500ppm is pretty hard. It comes to the tap directly from a deep natural well and is not filtered before use.
I flipped open Teaming With Microbes to review the role of phosphorus in microbial activity. Lowenfels notes that the immobility of phosphorus often confines it to the top 2" of the soil and if the microbiology is widespread and diverse, it will be available through the soil food web and "far reaching" fungal hyphae. He emphasizes topdressing with fungally dominant compost and mulching to increase the accessibility of nutrients and moisture content of the top layer of soil.
Think of this like a clogged sink overflowing onto the floor; without fungal activity at the surface of the soil, the phosphorus build up eventually creates an imbalance in the soil food web and problems begin. This issue was likely compounded by my plan to "fix" the fungus gnats as top dressing with perlite speeds the drying of the top 2-4" and thus decreasing microbial activity. As my dad would say; "Either unclog it or start bailing."
This seems to be the dilemma; 1. the slow process of reestablishing microbiology, or 2. the application of a new source of water.
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Although the water is hard, it's also nutritious for both plants and microbes and we have much success with it in our vegetable and flower garden. It is my belief that the non-nutritional application of EWC/molasses tea will reestablish microbiology and eventually resolve the phosphorus build up. Also, now that the fungus gnats have died and the composter no longer houses them, perlite at the soil surface may be removed.
The plant is budding well, trichome development is widespread, and the newest growth is thus far unaffected. Reestablishing the soil food web may delay harvest but this is Lowenfels' and others' recommendation for organic gardening.
All of this being said; if there is no improvement by the end of week 6, the two gallons of distilled water that were purchased yesterday will be applied immediately.
Edit; the majority of the perlite has been removed from the top of the soil. A very thin layer of EWC was added in its place.