I totally get the benefit of buildup from the plants perspective, it's the fish's perspective that I'm curious about here.
In the video it shows cories snuffling though a fair layer of detrius. That derius isn't all carried away by the current. It is providing an essentially infinite volume of water change, however, at least in a moving body of water.
I don't keep cories anymore due to losses (5 in 8 months or so, most spaced out), but I do keep quite a few otos. I've gone from water changes of 25% every two weeks (heavily planted Walstad with an AQ20 on a 20L, 50% surface gravel, 50% sand) to 25% every 4 days or so and a ton of flow and filtering (2x AQ50's on the same 20L). Filters cleaned (in tank change water) every month, substrate vacuuming "every now and then"....hence my question.
Haven't lost a fish for a long time due to sickness, so yay, but I'm pretty convinced otos are hardier than sterbai cories once they settle in. Then again, I may just know them better now.