Ok guys thanks for the input, lots of good ideas.
Part of me wants to get an eel, but if I got an eel, the species I'd want is a fire eel. But as far as I know, they can get up to 3+ feet? That doesn't sound so good in my 18" wide tank. A Peacock Eel would fit better (max size 8-12" I think), but I'm not too fond of their color/patterning. Can eels thrive in tanks where they are longer than the tank is wide? I imagine they can tolerature it more than, say, a Pacu that can't turn around.
The 2 reservations I have about getting an eel (besides what I just mentioned...) are that (1) I have a fine gravel and I'm not sure if an eel would be able to dig in it and (2) they are originally from Asia right? Right now my current stock are all from SA (unless JD is CA?) and I kind of prefer to keep it that way, but thats not set in stone.
I'm really not wanting to remove any stock, I don't think the silver dollar school would look as cool when cut down to 5 from 11.
The cory school is an option but I've never kept them before and honestly they never really struck an interest in me, but who knows, I might change my mind after some research.
I also like the idea of a single medium to large but peaceful cichlid (what are some more suggestions other than Chocolate cichlid?) or severum. I'll have to start researching severums and see if its something I'd like.
Thanks again for the input, I have some thinking to do
