ive heard all true eels are brackish to full marine? maybe some aquarium salt would help? do some research before you take my word for gospal tho... i had a manny piranha once that took over a month to start feeding! good luck
I added a small amount of 'tropical salt' the other day but I'm not sure what amount equates to brackish, and where to confirm I should do this...
Hmm a month for your piranha is reassuring as he is a big guy with lots of reserves.