Rhombeus Hit Chin on Glass

I was cleaning my tank yesterday and while siphoning the debris, my rhom suddenly became skittish and hit his lower jaw on the glass. It created a bruise on the front of the lower jaw. I've seen some piranhas with this on the lower jaw and some even call it, from what I recall, a Chimple.

Is it okay to place some melafix in the tank to make sure it heals properly and without a mark. I don't want my p to have that mark or chimple.

Thank you.

It didn't really hit the glass that hard. It didn't make a sound which would really worry me. It just made a slight thud but created that slight bruise. Piranhas are supposed to heal really fast. Melafix is safe for fish in general but I'm not sure if it's safe for piranhas. Maybe someone can confirm if melafix is safe. Can I use salt?

Given that the fish has only been with me for a little over a week, this is the second time I've made a water change. The first time was when I did it with the lights very dim (at night) with minimal skittishness. For piranhas, I think it's better to do water changes at night. What do you guys think?

Thanks!

My rhom didn't have a chimple before I did the water change. In fact, I made sure I chose a fish without a chimple when I got him. He doesn't have that habit of rubbing against the glass too.

Does your fish constantly rub against the glass? Does he have a chimple? I just don't like that mark on the tip of the chin. The mark on my fish seems to be fading/ disappearing.