Photo: Is this fungus? What do I do?

[Coldnorthtoy]

I've already posted this in another thread but I wanted to get this 'out front' so hopefully someone can provide me with an answer. I had him in the fridge for ~4 weeks - the last 1 1/2 weeks of which I was dosing the water with the equivalent of about a 79% Holtfreter's solution - and it pretty much all went away, but I may not have waited long enough - he still won't eat, and it's started coming back.

My water is pretty much perfect: Temp is 19, pH 6.8, Ammonia and Nitrites nil, Nitrates ~10 ppm.

Is this fungus, or something else?
What do I do?