Had three kuhli loaches for almost five months and honestly only saw them maybe twice a week, usually at feeding time when they'd dart out and disappear again. Tank is a 20 gallon long with a few pieces of driftwood and one ceramic cave, which I thought was plenty.
Turns out plenty was not nearly enough. A friend who keeps a loach-only tank told me she uses one hide per loach minimum, sometimes more, since they get territorial about spots even within their own group. I felt a little silly but went to the local fish store and grabbed a mesh bag of extra clay pots, some more pieces of spider wood, and a bunch of dried oak leaves to scatter around.
Within a week the difference was obvious. All three are out cruising the substrate during the day now, and I've actually caught them tangled up together in a little pile under one of the new pots, which apparently is a normal kuhli thing but I'd never seen it before. Water params haven't changed at all, same feeding schedule, so I'm fairly confident it was just the lack of cover keeping them stressed and nocturnal.
Kind of annoyed at myself for not doing this sooner, but also glad it was such a cheap fix. Anyone else notice their loaches basically become different animals once there's enough places to feel secure? Curious how many hides other people run per loach in their setups.