Re: puzzling, persistent substrate dampness
Well, unless there's some localized wicking from wet substrate seeping moisture into the drainage layer and back again in an endless cycle. Still, I don't understand why the relatively low ambient humidity of the tank (and definitely outside the tank earlier this year from the central air) hasn't depleted a significant amount of that moisture since what I'm adding doesn't amount to much.
I don't doubt that I have root issues on a few things due to their care prior to planting. I have certainly over- and under-watered my share of houseplants. Several have declined after planting, though, and I think lighting issues would have manifested differently - darkening leaves with perhaps exacerbated shed of older growth when under-lit and bleached new growth with smaller-than normal leaves if over-lit. I can look up the specs of the light fixture if it would help, though.
Given the popularity of the component ingredients (and ABG mix in general), I assume pH is not a factor; I know that pH can influence nutrient availability. I'm using distilled water, though the fertilizer water is mixed with tap that might be a bit hard. The occasional (once or twice a month, tops) fertilizer has generated improvements in foliage on plants seem healthy. It does not seem to help those that are struggling. Since I doubt nutrient deficiencies (mainly chlorosis) in the foliage would manifest from insufficient lighting alone, I'm assuming it's a root issue - the roots are not able to absorb the nutrients present. And that usually means too much or too little water; given these circumstances, I'm guessing too much.
I can feel the dampness of the substrate, and it stays dark in color, unlike the lighter coloration of the component ingredients when dry (plus several unused dry bags in storage waiting for other projects). It easily sticks to my skin when lightly pressed - especially the clay bits - though it isn't so wet I can squeeze any water out of it.
The plants still in the substrate are a mixed bag. Some are doing acceptably well, while others are looking piqued and a few have simply died.
Plants doing ok (not necessarily spectacular, but at least ok):
Syngonium wendlandii (or rayii)
Peperomia metallica (or similar)
Philodendron Wend Imbe, from a cutting
Pilea involucrata Moon Valley (or similar) from cuttings which have since rooted
Rhaphidophora cryptantha (from a plant I had acquired over a year ago and which slowly declined; I eventually took a few cuttings and the rest was a lost cause; there are four cuttings in the tank, one of which is doing far better than the rest and shingling up a piece of wood, albeit slow and with leaves still smaller than a dime)
Plants not doing well or declining, but not dead yet; some merely malnourished-looking:
Peperomia Rana Verde cutting
Ficus thunbergii (pumila Quercifolia) - grew very well at first, rooted onto background (foam + silicone + fine substrate covering), then began a steady decline losing leaves, chlorosis, and minimal new growth
Ficus Panama (took longer to get chlorotic than the other Ficus; not planted in the "ground" but rather in a substrate-filled planter pocket of a net pot in the background about halfway up
Adiantum Lace Lady (or Micropinnulum)
Elaphoglossum peltatum (though this wasn't a stellar specimen to begin with and hasn't been in the tank as long)
Gloxinella lindeniana (maybe it's going dormant? has lost lower leaves and is more floppy and a bit less richly colored than it used to be)
Piper parmatum (this one may have had issues prior to this, but I was hoping this might serve to rehab it a bit with better humidity than where it was growing...nope; new leaves at first but steady decline afterwards, and the leaves never even reached full size)
Selaginella uncinata and S. kraussiana