I assume you're dosing according to the directions, and not adding more?
My feeling is that dosing when you don't know what the cause is can be as bad as not treating, or worse. Imagine if you have a headache and someone gives you a laxative or a stomach tonic :-? , you'd probably feel worse and it would take your energy away from getting better.
Do a big water change and see how everyone is in the morning. If you have a spare tank you could put the ones with ailments in there and observe them for a while, otherwise it may be cheaper and less stressful on the healthy fish just to keep clean water and let the sick ones die, or put them to sleep with clove oil. I only say cheaper if it's a factor for you, it has been for me.
I've lost quite a few little fish over my time keeping fish and the best thing is to keep clean water and not to worry too much if you don't know what the cause is. Lesions are often due to infighting or are a symptom of another illness, once a fish gets sick they can be susceptible to fungus infections.