I don't know the background story to this (sorry), but yes, do a large water change. I assume this is a 10 gallon divided tank for the 2 males?
If your tank is cycled, I would do about a 50% water change to preserve the bacteria. If your tank is not cycled, do a 100% water change. If clamped fins were the only symptom, it was probably an environmental thing that was bothering them. If there were other symptoms then it might be something IN your tank.