Hara, indeed you have mention it, my apologies. Then it was you who i mention to others that i not remember who it was that had the fimbriated Eels with SF or even a jewel moray. For you know the aggression of the fimbriated Eels and yes, when not hungry, they look as if kittens in a litter. I do assume that the fimbriated Eels are still at their juvenile stages? In another forum i called the shots in what would happen and many people in that site believed me then only after what happen to this member for he was having the heart attack of his life. Now of course, you have these eels in a larger tank then he has his one fimbriated moray, but you are with a mix of four eels in a 120. Now i guess the 120 is a 5' long tank making it i think 18" wide is it? Now im sure that you have a great deal of L/R in this tank and i would guess no less then four power heads for your currents.
undertstand, you only just begun the mix of your eels in one tanks, so much is yet to come for the jewel with the SF, should do fine, but neither eels, the SF or the jewel can match the aggression of the fimbriated eels, Specially when hungry. And do believe that the eels are in motion at night and when the fimbriated eels become more settled in and aged a little more, they will move about day and night, for this eel hunts no matter in the wild day or night.
And i hope you not mind, that sense you have only a moray tank, i suggest that you do a weekly water changes
Unlike you done this 120 as a F/O tank, morays make more waste then most fish do.
I know that you know a lot in this hobby, but i been taking care of Morays for more then four decades and seen and heard much in that time. Now you can stay the way it is, only i suggest you feed those fimbriated morays well and i not know the size i believe they are now, but if they are feeding well, besure to have them on fresh strips of fish and octopus and squid, shrimps and no farm raised salmon, and at this time the year, you can only get pre-frozen wild and only buy what looks very good in color and only the tail section, it has no bones. You buy grouper, Cod, Trigger and not all at the same time, like when i feed octopus, i feed my dragons few each and that is it for the week. But the fimbriated eels, you need to feed then, least try and feed then every third day, they have an appetite some not believe and not bother with those silversides if these eels are feeding now, for the silversides are ok once to get your eels to begin feeding. But to offer then silversides all the time will prove an error with the fimbriated moray for they are mostly water then flesh and offers no nutrition.
Why i tell you this now, you are only in the beginning as yet and as i mention, i guess these eels are still in their juvenile stages. I like that you can be successful in the way you have it as now, but you do need to keep those fimbriated eels well fed.