It sure looks like hex to me. Did you clean up the pair? I didn't once and had a mess with deaths and stunting from flukes. Now, it a pair hasn't been cleaned up recently enough for me to remember when I did it, I do it again before they spawn.
I would like others with more experience than me to advise you but if these were my fish I would remove the slow growers (they rarely turn out) and watch for one more day. If you see the same symptoms in the same or other fish I'd jump on it by treating the tank with metro at the rate of 500 mg per 10 gallons and change up to 90% of the water daily. Wipe down the tank daily and keep up with this regimen for 12 days. Metro is the most gentle medication I know of so I wouldn't worry about the treatment harming the fry.