Treating ICH in Goldfish...how WARM is safe?

So it has been about a week and as of last night it looks like my favorite goldfish has suddenly taken a turn for the worse. The $0.16 comet is lying on the gravel and when he does move he flips around like he's very uncomfortable. I dropped the setting on the thermometer a few degrees and added even more bubbles but it looks too late for him. He doesn't have any visible ICH, but I guess the stress got to be too much for him overnight. The temp has been 83 for the last few days.
 
I tested last night and came up with a measureable amount of ammonia, perhaps 0.1 and the hardness was even higher than usual, off the scale. I did a good water change and I'll do another one tonight to protect the remaining fish. The tank is still finishing up a cycle apparently. I thought I'd avoided that completely by using water and dirty filter material from my other tank.
 
I thought I'd avoided that completely by using water and dirty filter material from my other tank.

Well, yes and no. You seeded the filter well using older filter material, but the amount of bacteria on there may not have been enough to keep up with the amount of waste produced by the goldfish. In other words, if there were 3 neon tetras in that tank rather than 2 fancies and a comet, there probably wouldn't be a problem with waste buildup - however, since goldies are particularly dirty fish, it may be that the combination of the ich, ich treatment and ammonia was too much stress for the comet. How do his gills look - are they especially red? What about the others?

If you comet does happen to pass on, it may be best to stick with the two remaining fancies for now. :)
 
The comet did die, yesterday, and I did not notice anything that looked really strange about his gills, but I did not look closely.

I have no plans to add anything to the tank. I am setting up another 20H in the wall at the bottom of the stairs and I'll be splitting these two remaining fish up into their own tanks. After that is all settled down I'll find something to be a bottom dweller in each tank and call it stocked.
 
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