Mine did fine with my florida gar, and would make good tankmates. I would wait until the eel is as long as the gar or larger before adding. gamr have been known to eat smaller eels though i have personally had no issue now keeping any of the larger species with gar at any size. I would suggest keeping the fire in the tank first then adding a gar not vise versa... ie letting the fire eel settle into a 75 or larger for a few weeks, eating ect well and happy. then adding a 12" florida. i would not keep an alligator gar with eels, and my cuban has gotten into scuffles with my large leopard eel a few times. fires being more docile in general might not be good for the more aggressive gars ( ie gators, cubans, or tropicals). but floridas are likely going to be fine.
I would also never put pvc in a gar tank... i almost lost a gar to getting stuck in a tube, use driftwood for the eel to hide. the only exception would be if you used 90s and where confident the gar could not manuver the angle.. imo not worth the risk.
