will clown loaches be ok with a clown knife? or would a jar. and some barbs be better? tank will be 210g? also if i get the jar should i buy it now so that it can grow with the knife?
Jars are known for being highly aggressive after a certain age/size. There is no guarantee that the Jar won't kill the CK later down the line. As for other tank mates, CKs are usually mellow and will get along with other fish. However, every fish have different personalities with some being more aggressive than others.
I have 3 ck's, 2 tf barbs and a huge 22" jar in together. No problems yet... But my results may not be yours. My big jar is a big baby but I have a small jar I had to put in a tank by himself because of aggression. I have one ck that likes to pick on the other ck's but other than that the combination seems to be working for me.