Molly fish tail fin looks odd.

[Annieg]

I have had fish in my tank tank for two months with no problem. Today I noticed one of my female mollies tail fin looks like strings are haning off. The water test perfectly. All other fish are fine. She is showing no signs of any distress. Eating and swimming normally. Is this fin rot?

 

[Colin_T]

It's excess mucous produced by the fish because something in the water is irritating it.

Check the water quality for pH, ammonia, nitrite and nitrate.

Do a 75% water change and gravel clean the substrate every day for a week.
Make sure any new water is free of chlorine/ chloramine before it's added to the tank.

 

[emeraldking]

I'm with Colin in this case...