Filter type for 60g bw tank?

[Chasnkevin4ever]

Hello guys, got a quick question. I'm getting a new filter system for my moray eels tank! It is a 60g tank between bw and fw, I'm looking to get a filter system that will still be able to be used when I turn the tank saltwater( slowly of course ). So I would need a fw/ sw filter, can anyone give me suggestions on what kinda filter I should use in there tank. Does anyone know if eels like moving water or not, like should I use powerhead or sponges or both? Any suggestions will help thanks!