I feel for you as I know how frightening it is to see their lil fins being shredded.
I have had to keep a VERY watchful eye on my sorority ALWAYS.
Sadly there is a bully in the pack. I took her out and then it just started over again as another decided to be Queen Bee.
Now I feel there is an almost tolerable bunch, but there is always a few nips and shreds for my lot. *sigh*

On the other hand .. they are still a joy to watch! They do have their happy and rewarding moments too.