Help with Silver Dollar

[LindaFish]

I have had my tank set up for 12 months. I have had two silver dollar fish since two weeks after the initial set up. My levels are good and no other fish seem to be having any problems. One of my silver dollars is having terrible fin problems! The large fin in the back looks like a "v" now with nothing in between. The dorsal fiin is also missing a great deal. It is eating and swimming around with the other one. I've heard of fin rot but not sure if just one fish can get it? Any suggestions?

[AngelMom]

We don't know what "My levels are good" means ... you need to post the actual test results (the numbers from the tests) for all the tests performed. At a minimum the results for ammonia, nitrite, nitrate and pH are needed. Additional test results can also be helpful as can any info on regular maintenance and supplements/additives used.