Trying to understand ich in my tank

[ReefCowboy]

Ive been reefing for many years, and would say over the past two, ive been more of a coral guy with no fish in my tanks. I have my current set up running for about 4 months now and have an sps dominated system.

I added two tangs, a yellow and a hippo about three months ago, and had a small true percula clown from before.
About two weeks iafter i had added the tangs, the blue hippo started showing ich signs. I realized i should have quarantined the fish, and learned that lesson the hard way.
The clown jumped out of the tank, as i found it on the floor one day. I tried catching the tangs to treat them, but realized i wouldnt be successful with an sps tank. I figued then would leave it as is and see what would happen unfortunately. Important to mention, the yellow tang never showed ich, no dots on body or fins ever noticed.

A few weeks of being left alone, the blue tang had not showed any more dots on its body. Because of ich's life cycle, i thought the new parasite batch would come full power and re-start the whole thing. Its been 3 months now and neither fish have any sigs of the disease, they eat normally, act normally. What is happening?

Im by no means trying to imply it went away as i know it is not a treatment, but being left with no solution, i cant really understand whats going on. Anyone can chime in what could have happened/is still to happen?

My tank parameters are always very stable so i can say the environment might not be stressing them as far as i can tell.

Here is a pic of the set up

[cabinetman123]

If your tank has good water quality and you feed good most fish will become immune it Ich. I have a 300 gallon full of big tangs. My last addition was a hippo tang that was about 7 inches long. When I added him about a week or so later he was covered in ich. The rest of the fish showed no signs of it. After a couple of weeks it was gone and never to return. Its been 5 or so months now. Those people who cant get ich under control got something wrong with their tank IMO. You must have things right.

[slief]

Hippo Tangs along with powder blue and brown tangs and notorious for developing a case of ich. Those are two tangs that I avoid like the plague just out of caution. Contrary to what Cabinetman is suggesting, most fish can break out in it if exposed regardless of water quality, feeding, health etc. I don't buy into fish becoming immune to it. It's typically brought on by stress of some sort and highly contagious in my experience regardless of how healthy or how long the fish have been ich free. While I've only had in ich outbreak once in the last 15 years, when it did happen it was devasting to an otherwise VERY healthy and established tank.

It all arose from a large water change that resulted in a water temp change of about 4 degrees in a very short time. In my case the powder was the first fish to show the signs and before I knew it, it spread like a wild fire. This on a very large 550G system that had been happy and healthy for several years. There was no treating the tank with copper as it is a reef and there was no catching the fish as it's a huge tank with nearly 1000 pounds of aquascaped live rock. I tried in vein every reef safe Ich remedy I could find. Fed well, aerated etc. The end results were the death of 75% of my livestock.. We talking 25+ fish from clowns to tangs to angels to cardinals and goby's.

It was a learning experience. I am very careful to match water temps now when I do large water changes. There are also certain tangs that I absolutely will not add to my tank regardless of how much I like them and the Hippo AKA Ich monster based on many peoples experience is at the top of that list.