I have a green spotted puffer who seems to be doing quite well. However, he recently developed black marks around his jaw area (one on each side). Is this something I should be concerned about? He's still eating...he really likes his bloodworms! I've tried feeding him dried krill, but that doesn't seem to tempt him anymore. Any ideas? The last time I tested his water, everything was good except for his ammonia level. I did a 25% water change to lower it...Any response is much appreciated!