Your water level is well below the substrate barrier and the substrate doesnt look overly saturated at all.
Exactly - it looks like the water is only covering about the bottom 40% of the LECA depth. That's great, that's a great water level. LECA doesn't really wick at all, so your substrate isn't going to be getting soggy - not from the bottom up, anyway. At this depth, that would be impossible. Having some
water in there is much better than having none in there - the key is, not too much. Wicking sucks.
If you can dial in your misting and watering so that you keep your LECA-layer water depth roughly about where it's at now (a little wiggling is fine
, just watch for - and if you see it, remedy - a steady uo or a steady down), you're in good shape.
Why do you suspect soggy substrate
Here, I'm intentionally truncating SM's question down to the substrate only (I'm not talking about the isopods or your search for reasons some of them died). Why do you think that substrate is soggy? It clearly is not...
As for your isos - sorry bud, it's something else.