juvenile seahorse

Hey guys! I've been building this seahorse tank for about 8 months now and finally got five juveniles! A couple of the bigger ones were shedding as I got them which I know is normal for juveniles but this one wasn't. Now after being in my tank for 48 hours I saw this spot pop up on its side...

I bought a couple of captive-bred Ingens seahorses online about three weeks ago. They are doing pretty well, but arrived being much smaller than I expected. (The website claimed they were "medium" sized, but these are really more like small juveniles IMO). So, instead of putting them in my...