That is indeed columnaris. Columnaris is actually a bacterial infection, not fungal, but because it looks cottony kind of like a fungus it is often called that.
Keep temp as low as possible (Whatever you do though, DON'T raise the temperature, that's a death sentence) and continue treating with the Fungus Clear. Check your water parameters. Have you introduced any fish lately? Columnaris spreads and kills quickly but is not all that common in a well maintained tank.