Hi! My several year old angelfish in my 28 gallon freshwater tank has rapidly developed hole in the head over the past few days. She is eating fine, and doesn't seem stressed. I notice a white nodule on her head the other day, and while she was feeding I rubbed it. It came right of and exposed a small red pinhole. No there is a much larger hole off to the side of her head. All I have done so far is added aquarium salt, which I just found out is bad for corys and plants... Oops.

I only added 5 tablespoons instead of the recommended 7. Looking for a little direction on this.
I have basically answered all of the questions in the sticky here:
My params are (according to API for the first 3, and Tetra for the last 3):
NH3 - 0.25 (I just swapped a sponge, so my bacteria are probably mad, it's always at 0)
NO-2 - 0
NO-3 - 40ish (I know right off the bat people are going to go after this, but I have been battling it for a long time, it never goes down. The prime detoxifies this though, so it shouldn't be harmful)
pH - 6.5-7
KH - 2-
GH - 8
Temp: 80
The tank has been set up for several years, with the most major move being a year and a half ago. Other fish in the tank include 7 gold barbs, 5 black phantoms, 4 razboras, 12 small neon tetras, 3 botia loaches, and three 3 small albino 3 corys. I have had most of the fish for several months to a yr + and the angel is at least 6 or so years old if not more. The tetras, 2 of the corys and 4 of the bards are the newest addition, with in the past couple of months, so they are all still babies, and the rest are adults.
I have some small java ferns and a medium sized anubia in the tank, which are doing pretty well, considering I don't accommodate for their needs too much compared to my other planted tank. The only fert that I add to the tank is flourish, about once a week.
I am using an older whisper filter with bacteria sponges and carbon, I tend to rinse the sponges in the removed tank water every week, and replace them when it is not possible to clean them or the tank conditions suggest a replacement is necessary.
My tank receives natural sunlight from two apposing windows during the day, and I use 2 5k rated light strips.
I have been doing 40%ish water changes every week, and gravel vacuuming, and using Prime as a water conditioner. The increased frequency of water changes and using prime instead of stress coat are the only things besides flourish that have changed lately... and those seem like positive changes to me!
I feed once daily with Tetra brand flakes.
Here are some amazing photos!
The Angelfish (Kahlua), you can see the chunk out of her forehead a bit:
And the tank itself: