Why are blue green chromis' impossible to keep?

i've had one for a month and yes, the clown chases him when hes not fed a lot. the greens dont seem to ever eat to the point where they are fat. and mine will only eat crumbled up flakes. i think his mouth/throat is small. he seems to be fine though. i just wish he would get fat like other fish.

 

I had 4, and only have 1 left.. they would fight with each other and other bigger fish would chase if they havent eaten in a few days.. I've read its good to keep 5 or more in groups that are odd numbered..

 

I had three. Then one jumped in my overflow and was stuck in there for a week until I finally managed to get him out. Long story short I believe the stress of this caused Ich, which in turn the other two developed. I now have 0

 

well im in my 5th week and still have all 9.. hoping i keep it that way... they eat like hogs thats a fact.. im guessing they are such passive fish that anything takes on them.
i can even take a fish out with glass. and the wont try to scape. i can even take them with my hand and they wont go away...

they are pretty cool and fearless yet to passive of a fish.