I have 35 in my 200, the more you have the more active they are.
I started with 2 a couple years ago or so. I would have got more but the LFS only had 2 at the time. I've slowly added more and more. I recently got 15+ at once and the activity increased even more. With less than 10 they pretty much hid all the time if given ample hiding places except when feeding. Now with this many it's a constant show of loaches swarming around, I suggest 25 as a minimum if you have the space. They are very entertaining to watch and during feeding when you have a bunch all the clicking sounds they make are awesome.