White spot on dorsal fin?

[GWdiscus]

I noticed this spot on the dorsal fin of my largest discus, a yellow 4.5", in a 75-gallon tank, with 8 other smaller discus of various types, on a bare bottom tank with 4 potted plants. I was out of town last weekend and returned to find this white spot. This discus in question has shown no other signs of stress.
Any suggestions or commits?

Thanks
Michael

Ps
I'm trying to post a picture for the first time, hope it works.

[GWdiscus]

Here's another close-up picture.

[Carol_Roberts]

Looks like a bit of damage to the ray that has fungused. Salt and water changes should clear it up in a week.

[GWdiscus]

Thanks Carol, you're right, the top part of the ray is missing. I normally put in a teaspoon of ocean salt per 15 gal with daily water changes. I'll increase the salt to about 1 teaspoon per 7 or 8 gal.
Thanks for your input.
Michael