I know this post was a few days ago ... but I've only just popped over.
I have six chain loaches in a 20g tank and they're fine. They have a couple of pieces of very craggy bogwood in there, which they love sitting on, in or under.
I used to keep them with tiger barbs, pearl and zebra danios and I worried about them when they were little because I didn't think they were getting enough food. Used to use a pipette/syringe to squirt food just in front of their noses. Once they've grown up a bit, though, they're quite capable of fending for themselves. They swim up and catch food in mid-water.
They're just in with the tiger barbs now. I've moved the danios to a bigger tank.
The only thing to be wary of ... is if any of your other fish are sick. The chain loaches will try to get a feed of slime (or even an eye!) if any of the other fish slow right down. I wouldn't keep the loaches with any slow moving fish and I'd now isolate any sick ones as soon as I noticed a problem. One of the barbs lost an eye three or four months ago and, although I have no proof, I suspect a loach caught her in an unsuspecting moment. Doesn't seem to affect her now though - she's obviously learnt a lesson.