Sick Apisto - Is This Fungus?

We survived cycling. Everything was going so smoothly. Then today my little boy woke up to a sick apisto. It's his favorite fish. The tank mates all look and act normal. There have been no changes to the tank in over a month. I have at least twice the filtration I need and the tank is 25 gal. We use the API master kit and test regularly, including today. Levels are all zero and always are. I did a 50% water change this morning. The tank has the apisto, 6 cory cats and a little angel. It has been difficult to get pics of this guy's ailment, so I'm  just sending what I've got. Thanks so much!

Can you describe the symptoms please. 
It's rare to have a nitrate reading of 0. Do you have live plants in the tank?
 
 
Welcome to the board.

Sorry forgot you said fungus in the title.
It's hard to tell in the pics you have posted but where is the fungus on the fish?
Does it look like cotton wool?
 
Blown the pictures up now. Do you mean the white patch under the dorsal fin.
If so does it look like a bleached out patch, or cotton wool. As it hard to tell in the pics.

I know the pics are terrible. I took tons and none are good. Yes, the patch below the fin. Its white, but not cottony looking. Its not raised up at all. In some light it is really obvious, but if he turns a different direction you can't see it well. He was fine for weeks. Normally he sleeps under the log, but this morning he was lethargic and up near the surface between the filter and the glass. When I got him to move, I noticed his pretty colors were dull and pale. And the white spots were there near the fin. His fin is also clamped down now, but there may be a spot on the fin too. He was hungry and he ate normally. He is swimming now. I don't know what to say about the nitrate. It's always yellow. I had one time a few weeks ago when it barely had an orange hint. Its not heavily stocked and we change water regularly. That's all I can say about that. 

It looks and sounds like columnaris.
You said spot on fin do you mean a patch the same as under the dorsal fin, Or a spot?
 
Can you isolate him as you will need to medicate and the medication will wipe the good bacteria out in the filter.
Maracyn, Maracyn Plus, Tetracycline.

Another link for you.
Scroll down to saddleback columnaris.
http/www.americanaquariumproducts.com/columnaris.html

I can get a qt tank set up asap. I have two filters now, so can I just move one over to the qt  temporarily then move it back to the main tank after? I can't see what's going on with the fin because its completely clamped down. When I said "spot" I meant "area". It looks as though the patch may continue on up to an area on the lower part of the fin. But since the fin is all clamped I can't tell. Plus he has decided to only show me his good side all day today. Makes it trickier. When you say Maracyn, Maracyn Plus, Tetracycline, are those 3 different treatments I need, or any one of them? Will I find that at Pet Co or equivalent? Thanks a lot!

I would remove the mature filter media from the filter as the antibiotic is just going to wipe the good bacteria out anyway.
Just add some filter floss.
Run the filter if you don't have an airstone as medications reduce 02 in the water.
 
Just use one of the medications I've listed.
Maracyn a gram negative antibiotic.
Maracyn Plus is a gram negative, and gram positive antibiotic.
Tetracycline is a gram negative, and gram positive antibiotic.
 
To cover all bases I think I would probably go with Maracyn plus, or tetracycline.
If you can't get hold of any of these medication from the LFS as for a antibiotic that 
treats both gram negative, and gram positive bacteria.
 
Also set temp in these instructions below.
 
 
COLUMNARIS
 
The hospital tank should be heated to approx. 74 degrees. 76 and above is the ideal breeding temperature for columnaris. Though there is some dispute over lowering the temperature, my experience has been that 72 is too low for the medication to work rapidly, 76+ causes the disease to breed more rapidly than the anti-biotic can kill, and 74 is "just right." Remember to keep this temperature stable!

Thanks so much for all your help!

Good Luck.