I've got 2 clown loaches in my 30 with a couple of kenyi cichlids. They are ~3", up from ~1" when I bought them from walmart a while ago. I originally had 4 small loaches in a 10, but ick broke out and these were the 2 survivors. Once you get past their first month, you are pretty much in the clear as they usually live for years and years and years (I've heard of some 40 years old!, although thats probably pretty rare for most loaches) barring horrible ick outbreaks (keep the temp at a stable 80 to prevent this!). For a school of ~5 clown loaches, a 55g would be good for a few years, but they will outgrow it. They are very fast and like to swim around. Keep plenty of hiding places, and the sides covered, and you'll see them alot more.
So real quick:
*Salt Bad!! Don't use it!
*Need a varied, high protein diet (blood worms and omega 1)
*Most I've seen like hikari algae wafers
*Most seem to also like zuchini and peas
*They love snails!! I intentionally raise and release them for the loaches to hunt down!
*Keep up with water changes, they are sensitive to bad water conditions
*Lots of hiding spots
*They can harass slower less aggressive fish while trying to school with them
*Clicking is a happy noise!
*In case of ick, use a half dose, or special directions if on the box
Thats most of the important stuff I can think of...