I'm sorry to report that Owen passed yesterday. I did another 25% water change early this week and he just never showed any sign of improvement.
What first caught my attention was the bristle worm in the tank seemed to take an interest in him about the same time he stopped eating. Prior to that time, anytime the bristle worm would come around when Owen was eating, he would push him away. The first sign that there was something going on was seeing the bristle worm hanging out by Owen's den. I noticed that about the same time I noticed he wasn't eating. Even the last crab I saw him kill, it wasn't the typical parachute over the crab type of kill. He grabbed it with his arms and kind of held it for 5-10 minutes before killing it. At that time, I didn't think much of it but that was the last time I saw him kill a crab.
I'll post a video of him holding that crab later on.