trying to identify

what's on my fish's tail. I got a few more pictures, asking on the forums... Quite a few barbs have split tail fins now from all the darting around to avoid capture yesterday, I didn't want to stress them out anymore so didn't try to give them another salt bath.

More alarmed now because although all the barbs look fine other than these two with marks on the tail, my smaller striped kuhli was swimming in an odd, twisting motion across the bottom. It took me a minute to realize he was probably flashing, scraping himself on the gravel from some irritation. He was near the front but close as I looked I couldn't see any marks on him. I tested the water quality- nirates are ten (I've been doing extra water changes).