There are a good number of dwarf morays that grow even at 8", but here are five that grow even less
Gymnothorax parini Under 3"
Anarchias leucurus 4"+
Scuticaria okinawae under 4"
Anarchias galapagensis 5"+
Anarchias allardicei 6"+
Eels over all are very hardy once they adapt to captivity, and the main key is their water quality and a nutritional diet over all. But perhaps you heard from time to time people lost their eel from ich
This in most cases is because hobbyists over stock their tank with as many fish as they can put in their tanks
Eels can and could become overly stress out from a crowded tank
Just for the fun of it, which moray you think is the longest of the species