In oscars it is HLLE
, not HITH, and it is usually caused by poor water and food quality. It is not a pathogen like HITH and other illnesses. Although feeder fish can contribute to poor nutrition, they are a symptom of other issues, not the lone cause. A high quality pellet is the best staple for any diet. Enough water changes to keep the nitrate concentration under 20ppm before a water change willl keep the water quality high.
If you have multiple cichlid together it is best to raise them together, this is the best way to help make sure they get along.