One that you didn't mention is the black kuhli loach. Lots of people seem to like those.
They don't need sand to be happy. I had a couple of kuhli's in a 10g with gravel, and they were perfectly happy. I actually some them out and about quite often. They might hide at first, but I imagine you'll see them quite a bit once they get comfortable in their surroundings.Are kulhis really out enough to enjoy? Thought I'd heard that they hide a lot. Had also been told they need a sand substrate to burrow in. Will they be ok/happy in an eco tank or does it really need to be sand?
The larger the school, the more comfortable they'll feel in your tank and more likely you'll see them out and about to enjoy them. With your 55gal, I'd probably shoot for 8-10.Cool! That's probably the way I'm going to go then. I really like them, just had in my head they wouldn't work in my tanks!
And then there are guppies... The Sansa Stark of fishI think all bottom feeders are ugly. The only one I truly like is the pygmy corydoras because they're small and they just sit there. Their ugly catfish features are too small to see unless you look really close.