True Tale of Hippo, itch and immunity

[Uncle99]

This is what just happen to my hippo and I want to share it.

I have my hippo for 4 years, got it in November 2019, along with a six line wrasse.
They were the last fish added. My tank is a 125G, 6' long and I inherited it around 13 years ago along with a four stripe damsel which is still with me.
I have never quarantined anything.
I have no coral, but I do have peppermint shrimps, hermits and various snails.

I went out of town for 2 weeks in October and came back on the 30th. My daughter fed the fish daily during that time.
When I came back everything looked fine.
However on the second of November, my hippo behavior was strange. He swam like he was nervous, and hid more, but ate fine. On the third, something was definitely wrong, behavior was very off and I started to see quite a lot of white dots. On November 4th, it was more white than blue, absolutely covered with ich. Never saw him like that before, nor any fish.
It was hiding most of the time, but ate very well. No other fish showed any sign of ich. I was getting very concerned, and pondered what to do. I had no medicine, and no testing device. I did have a 20 G aquarium with lots of macro algae and snails in it, but no fish. It has been fish less for 2 years, so I was wondering if I should try to catch my hippo and put it in that tank.
But, ich was in the tank anyway, and not other fish were affected. No way all my other fish would fit in that small tank, and the rabbit fish would have decimated my algae in not time. Plus I did not want to stress my hippo any more nor the other fish in trying to catch it. I had seen my hippo with some ich on him, on and off, so I decided to see if he could cure himself.
Plus my hippo was still eating very well, though hiding all the time except at feeding.
He was still hiding and eating on the 5th, did not looked worse. On the 6th he looked a little better, and I was wondering if I was imagining it. On the 7th, a lot of the ich had disappear, and fish was a lot more active, though not back to normal.
20 days later, and my hippo is now back to its normal self, very active. The ich is gone.
I am convince that his immune system won, I did not give him any treatment, did not even changed the water.
I feed my fish a variety of Hikari frozen food, LRS fish frenzy and nori, plus fresh macro algae when I need to trim my other tank. I fed only LRS food while my hippo was sick.
I know ich have cycle, so that is why I waited before writing about it. But right now my fish look completely cured, and no other fish have been affected.
I am still watching him, and will see if it happens again. I have no idea why it happened suddenly, as nothing was added recently in the tank. But I did loose a green chromis recently.

Identical situation. 5 year old hippo. Twice now. No way to get fish out without destroying the entire system.
Once @ 3 years, again @ 4 years.
Both times the “Cycle” lasted for about 3 weeks in total, from spots to clean.
No other fish ever caught it.
Maybe lucky?
IDK but great to hear of your experience.
Like you said, low stress environments and good nutrition go along way at defeating this enemy.