Got a strange ich question

[flitabout]

So I haven't added any new fish to my tank for roughly a year, and I am seeing what looks like ich on 2 of my cardinal tetras. I am at a total loss. Is this even possible?
Tanks parameters are:
0ppm ammo
0ppm nitrite
20ppm nitrate (I am lucky to get it down that far even heavily planted)
Temp is 75F
I do 50% weekly to bi-weekly water changes
I use prime water conditioner, it's a 55g with a marineland 360 and a Aqueon HOB rated to 40 I can't remember it's been to long. Dirted with a black blasting sand cap, heavily planted with a 5 white skirt glofish. 6 Cardinal tetras and a goldfish (Yes I know Bubbles shouldn't be in there) My daughter brought it home from the fair last year. The Cardinals are getting old and are all over 2 years same as the glofish which are 2-6 years old. I lost my 5 year old bristlenose pleco about a month ago. This tank has been running for the last 5 years. The goldfish was the last addition and that was over a year ago. So I am at a loss as to what is going on with the cardinals. Their fins are also looking pretty rough.
Any ideas would be greatly appreciated.

 

[SaraB]

Did you add any new plants?

 

[BBradbury]

Hello flit...

If the tank was mine, I'd add a bit of standard aquarium salt to every five gallons of treated tap water. A teaspoon or two should do the trick. This will stimulate the immune system of the fish and discourage the growth of any parasite. Add the salt to the water until you see improvement in the health of the fish.

B