[Fin Rot on Goldfish]

The tank only has sand and some plants, nothing sharp. 

[Fin Rot on Goldfish]

I noticed that my goldfish started getting these tears in his fins, so I followed the instructions in this video (https://www.youtube.com/watch?v=wICf_0o6ys4) to treat for fin rot using maracyn and ich-x in a hospital tank. After the treatment I moved my goldfish back to the main tank, but now a few weeks have passed and it doesn't seem to be getting any better. What else can I do to help my fish? 

ph - 8.0

am - 0ppm

ni - 0ppm

na - 10ppm