There is no concrete answer to this problem. For myself , I feed them once a week with small piece of cut prawnmeat . This frequency is ok but from my previous experience I saw them swallowing it so fast thinking that they are hungry and put in another pieces landed up with perhaps an indigective problem and it start to get white and fade. I told myself to feed them with only one piece and my sun is now doing well.
Hope this idea help you in any way