Both are messy eaters so make sure your filtration is up to par before adding anything else to the tank. The bio-wheel you have should be able to keep up with keeping nh3
levels near 0 but you still will probably have to siphon your tank once a week when you do the pwc
. I’d wait at least 4 weeks after adding your puffer to the 55 gal
to add the eel. Don’t forget to acclimate the puffer from your 10 gal
to your 55 gal
I noticed you added some more photos
I would also get at least 2 ph for circulation/aeration since you have your tank covered. Also you will need more rock in order to provide a place to hide for the eel.