My next project is to create a series of undergravel tunnels for the loaches out of PVC pipe and connectors. The connectors would curve up to poke above the gravel as entrances to the tunnels. I was thinking of an elongated sideways H shape to fit the tank, with a few shorter pipe lengths buried around the tank.

Does anyone have tunnels like these? I'd imagine with so many more hiding places added, I could get a bigger population of loaches.

Yeah, I've got a couple of short, straight tunnels. I've siliconed gravel over them, and inside them, so they often cannot be seen unless you know where they are.

Your idea is interesting, having them go down, across and, up. I could see myself having one in place by the end of the week! Any concerns about them filling with waste, or dead fish? I guess they'd be easy enough to clean by siphon.

I would be concerned about fishie business too - but that sounds awesome otherwise! I am gathering ideas for my new aquarium that I am setting up, and this sounds like something work giving a try!

Sorry for the long wait between then and now to post my reply!

About cleaning, my plan was to take the tunnel(s) out monthly or so, give it a good scrubbing, then re-bury it. My bottom feeders all do such a good job at getting rid of a fish body that often I don't even know that a fish has died until I see a bit of skeleton. So I won't worry too much about bodies piling up if any happen to die inside a tunnel. Ew, little carrion cannibals, they are!