Your system being so new, my feeling would be that the system is still balancing out and the fish are stressed. I would suggest dosing seachem metroplex just incase of disease, vitamin C for the stress mixed with seachem focus with the frozen food for 14 days.
I had this happy when I first set up my current system. 4 fish just passed mysteriously without signs of ick or brook.
Ok I have pazipro now at home but will look for the sea Chem products. Everyone was swimming and eating fine so not sure how they were being stressed. Any thoughts on the fading top half color on my clown? Didn't eat today and hiding in a corner. Gramma didn't eat either and hiding inside a rock all day.