Yeah, wicking was what I was assuming also. The puzzling thing for me is that I have hardly used the drainage layer as a water reservoir (especially since I noticed the trend of damp substrate awhile ago) and I definitely haven't deliberately put any water down in that layer for over a month (possibly even two...these weird days are messing with my sense of time).
I understand the idea behind the wicking physics of smaller particles though - capillary action and all that - though I admit I didn't give it much thought. You're right - these are on the small side relative to something like LECA balls. I'm just perplexed by the fact that, given how relatively little input the base has had, water-wise, why it hasn't dried out measurably in the past several months since being installed. Especially since the ambient humidity of the tank seems fairly low during the day (about 30-40% winter, 50-60% summer). Did I accidentally create some sort of self-contained system of water cycling just in the substrate and drainage layer (in other words, insufficient evaporation), where the initially soaked substrate slowly drip-drains into the drainage layer, only to be re-wicked back into the substrate?
The Growstone I've used for other things comes in multiple particle sizes (around a quarter inch up to an inch or more), and while that's just one brand of the stuff, I swear everything I see that looks like this is all the same material, just sold under different brands. If memory serves, it's recycled glass, and resembles pumice or a fine lava rock but is lighter in weight. In other applications, I've used the finer stuff as a potting soil amendment for succulent containers. It doesn't float like perlite does over time, and I think it's pH neutral given its composition. Anyway, the particular material I used was from Josh's Frogs (https://www.joshsfrogs.com/josh-s-fr...r-1-quart.html
), though I have some unused from NEHerp that appears to be the same exact stuff, just the larger ~1" grade. Ditto Black Jungle, though it's a different color.
I did include a siphoning "port" when I installed the drainage layer - it's just a short vertical section of corrugated tubing that I can stick a turkey baster into in the front right corner - easy to access. Trouble is, there's nothing to siphon out - no free water. Presumably that's because it's locked-up where I don't want it. I do not have a drilled drain because I'm using the tank as-is and am not experienced or equipped (or ready to try) in drilling glass.
So, I'm wondering what the best approach is going forward. Do I pull out everything (terrestrial) and re-do the drainage layer? (With what, if I don't use suspended egg crate...LECA or...? Or is propped-up egg crate best?) Or just work with what I've got and use emergent aquatics, in the assumption that it's staying damp enough that they should prosper w/out free water for their roots? I do have a Hemigraphis repanda
in there that initially did well (may have just been a "thank you for taking me out of that tiny pot" growth spurt) and is now looking so-so.
I realize the trouble I'm willing to go through to fix this is up to me, but outside of that, are there other reasons to either re-do things or adapt the plant palette instead? I'm assuming the substrate mix itself isn't an issue, considering how prevalent it seems to be in this hobby.
Interestingly, the Growstone mixed into my succulent soil does not seem to hold moisture - if anything, I think it dries the mix out faster (a bonus in that case, certainly). When used as a topdress on some of those pots, it also seems to dry quickly - perhaps the better air circulation?