FYI: Don't put shells with big open twists into the center with africans.
I saw my male kenyi get spooked and shoot way inside one, totally stuck. He's my best 'Save' ever: I held it & him in a little bucket and kept swishing water in & out of it, sawing a square off the shell with a dremel.. thought for sure he'd either be dead from oxygen deprivation or me slicing him, but I got him out unscathed and he survived. It took a LONG time after bedtime. I still have him AND the shell with the escape hatch! I love that darn fish, he's mean and survived more than 1 mismanagement wreck. He eats nicely from my fingers but tears me up if I put my hand in his tank. he scrapes skin off!
Anyway, choose shells carefully. everybody told me they would've just let him die.