Wow, I must have gotten pygmy clown loaches then. 6 inches in 6 months is so far away from the truth. I hope you are not telling anyone at the LFS you work at this kind of stuff.
I have four in my 55 gallon tank and have had them well over a year. They are still around 4 to 5 inches and extremely long lived. I would believe 30 years. Thinking back to another posting I read somewhere (will try to find it and get you the link), one person had a clown loach for over 10 years and it was in the 6 to 8 inch range, but still a very big 6 to 8 inches.
This is why many people get away with keeping clown loaches since they do not out grow their tank as fast as most fish do. I keep four, like I said, and they are fine, even with my cichlids (yellow labs). They are kind of shy though at first, but you can help them feel more comfortable by offering a lot of hiding places.
Clown loaches do love blood worms. Mine seem to be able to smell them when I feed my tank blood worms, usually on a once a week basis. They are 'micro-eaters' and will eat really small amounts usually quite a few times a day. This makes them good for picking up any food that may have fallen into your substrate.
They are very peaceful, usually, but they do have a sharp bone under their eyes for defense. This could be bad if you have fish that might pick on them a lot because the clown loaches can hurt them. They are also scaleless fish and this creates challenges when treating for ich or other problems with medicines. They really need to be in groups, otherwise you will never see them since groups allow them to feel safe enough to get out and about. I have heard as little as three loaches as a minimum, but as much as 5 being the least amount one should have in their tank. I obviously went with the middle ground and got four.
Great fish though and full of personality!