2 things come to mind, first how is your water quality, an elevated pH can cause symptoms like that. If your pH is good than it looks like a very early case of finrot, in that case Maracyn, Binox, Furanase, TMP sulfa, and several other meds should clear it up but it is usually caused by a high bacterial load in the water so you might want to increase water changes on increase filtration as well.