Looks like he got stuck behind something and was damaged wiggling out.
Is your test kit used by date good? Going by your food choices & feeding schedule a weekly 30% water change and nitrates <10 is impossible as they would constantly be climbing. For example let's say on water change day your nitrates are 10, you remove 30% of the water effectively reducing the nitrates to 7. Over the next week they gain 1.5/day, and they're at 17 the next 30% water change day, and so on. Without a near 100% weekly change nitrates never get close to 0 and are therefore are always climbing.
All that to say, either your test kit is out of date, or something else is up...