The fish is Hemigrammus ocellifer, we were discussing the discoloration of the anal fin., the white bit.
Pebbs, it's really hard to see, frankly it doesn't look bad. This and a few other characins do have a whitish leading edge to the dorsal and anal fins. Yet you say it is getting worse, which is odd, however, I trust your judgement.
Fin rot is a bacterial problem and is a feature of badly maintained tanks really, and I don't think yours are. Fungus tends to look like fungus, it's lumpy or hairy or, fungusy looking, and you say this is not.
Are the Hemi's still obviously "out of balance"?