Seen it with black ghoust knife, I currently have a bgk and African knife with my clowns but soon as I get a chance I am moving them out. The African is aggressive.
Angels is okay.
Zebra loach is good.
Clown knife is known to be aggressive.
Black ghoust knife is okay.
clwn knife is only 5" rt now. have him in the 75 gal rt now till he gets big enough to put in my 150 or 250.. Things in those tanks would eat him rt now since he is still small. And between now and then, if he does show any aggression, I have a 40 gal Ill be putting him in.
BGK - No worries, unless the loach tries hiding where the knife hides. I have mine with cory cats(way smaller than a CL)
Clown Knife- I would say go for it. The CK I had till about 10" was reclusive, but I have seen the aggressive side of this species too, but bottom dwellers usually stay off the radar.
Angels-Never had these, but again, the loach won't ge in the same swimming area as the angel, should be fine.
zebra loach-possibly fine, but most likely won't school with the CL.
Clown loaches need to be kept in shoals to have them behave properly, plan on 3-5 minimum in your tank...From most every post I've read about CL's.