I had the same issue in my planted tank, my problem was the water in my office had to high of a PH, Harlequin Rasboras do best in a PH with 6.5 to 7 PH, I am think that is your issue. I added Poland Spring water to my tank when I did a water change and it brought it down, this might help you.
Bump: When my PH was too high the fish would not eat and breath very heavily, they would swim in circles before they died, if this is what is happening for you then I highly recommend lowering the PH.
Bump: When my PH was too high the fish would not eat and breath very heavily, they would swim in circles before they died, if this is what is happening for you then I highly recommend lowering the PH.