At this stage, it looks like the fish in your QT have developed a certain amount immunity to the parasite, which is why you're no longer seeing any active pustules. Acquired immunity has been demonstrated in a bunch of fish in the literature, but the parasite is definitely still in your system.

If you have no plans of going through the extremely intensive and time consuming process of taking the remaining fish out and treating them in QT while fallowing your tank for 10-12 weeks, your best bet for re-stocking is to not buy any fish that are known to be highly susceptible to ich, as it's in your system. IE, don't buy any more tangs.

+1

What people don't realize is that there is often different strenght of ich and some strain might be mild while other are very strong and active and will multiply like crazy and overcome any fish, stressed or not.

It's the same thing with bacterias. You can have some vibrios bacterias in an aquarium and it wont affect anything but given the right conditions those bacterias could go wild and cause brown jelly on many corals.

Ich is one of the major fish killer. I think it kills more fish than any other disease put together, velvet included. It's just too common and people often don't do a thing about it and let their fish die.

You don't get it? well that's because it is not the right way to do things. It is not when the fish are full of ich and on their way out that it is a good time to treat, it is when they arrive and relatively healthy. That's why quarantine is so important, so that one can treat sick fish either as prevention or at least on time.

Of course if the fish are dying and breathing already so fast and still suffocating, catching them might finish them off...but if they are at that point they will probably die anyway.

Fish are strong, very strong. Imagine the traveling in small bags that they have to do? Problem is that ich is attacking their gills and they suffocate. That's what kill the fish, not being handled, not being cought, not being transfered between tanks.

The second killer of fish in quarantine is bad water quality and ammonia. Those are very easily handled with products like Amquel.

I got the same problem like urs. My yellow tang start scratch ing with sand and rocks. I start giving garlic food and set the 15w aqua uv sterlizer. Lets see what happend. I know uv sterilizer wont grabe ich from fish. But what ever will go in. Will die. And also I got skunk cleaner shrimp.

I am not taking about pre-ich QT over there but about post-ich QT; just thought about clearing it up :)

Yah I do have problem understanding many school of thoughts in this hobby ;) Well if one wants to post QT the fishes and leave it fallow for more than 2 months; its their tank and they are more than welcome to do it. I did a lot (and I mean A LOT!) of studies when my tank had ich and guess what worked: let them just heal by providing them with proper care. And why is there so many school of thoughts, even with just one disease like ich? Because different things worked for different people and everyone just thinks their method is right. QTing worked for some so they promote that while old school method worked for me and hence I promote it. :)

^^^ Wisers slow clap for mrhasan ^^^^^

here's food for thought.....wildlife biologists have long known that a certain percentage of caught and released game fish die from lactic acid build up due to the stress of being caught.....why are our fish any different?.....I QTed for a while and had no better results than just putting the new fish in the display.....every time we put a net to our fish we cause lactic acid build up that could prove to be fatal.....I feel that playing musical tanks with a fish is putting it through more than is necessary......if you are observant and make good decisions buying your fish you will greatly lessen the chance of introducing something nasty....

I know the idea seems stressful, but the fish that die from lactic acid build up in sport or commercial fishing go through a significantly more acutely traumatic capture process than what fish in a properly designed quarantine procedure will ever experience - either being smothered half to death in a huge drag net where they are trapped for hours trying to escape, or are hooked through the mouth and pulled from the water fighting the line with every ounce of strength they have for as long as possible. Scooping fish up quickly with a net (or better yet a tupperware container with holes drilled in the bottom) isn't really comparable, even if you're doing the tank transfer method and are doing it every few days. Not QTing is a method that works fine until it doesn't, and when it doesn't the amount of temporary stress your fish were spared by not QTing them becomes a moot point because they're dead. I would never criticize someone for not doing it because it's an annoying and time consuming process (I never used to), and if you're lucky it works fine. But I also understand how quickly one can become a quarantine convert when you've had a near tank wipe-out due to parasites.

If you don't quarantine new fish, you are actually putting them through more stress, I believe. Besides the disease prevention, while in the QT new fish have a chance to be acclimatized to your DT water (prior to the final transfer) and new foods. They then have a chance to become healthy and strong before going into your DT.

Otherwise, if thrown into the DT immediately, they may have to face hostile existing tank inhabitants (like my yellow tang) while in a weakened state, and not used to eating the new foods. If that isn't stress for a fish (and the aquarist watching all this), I don't know what is.

Moving existing stock from an infected DT to a QT is a whole different story, though. My problem would be just in trying to catch them. So yes, I would first try to feed them well and hope their health and immune system carry them through.

But the real solution, which I keep preaching, is prevention, by QT'ing new fish. That is the best for new fish, and for protecting your DT. And it is so easy, which is why I don't readily accept lame excuses for not doing it. I have a 30g QT running all the time, with a canister filter, and water changes are done using DT waste water (from changes), so it costs me next to nothing to keep running and available when I need it. And I use it a lot, actually, sometimes for new shrimp and corals, too (no hypo for them, of course). It is a lot more work to maintain a refugium, actually, as I have done that, too.

Not QTing new fish is like playing Russian roulette with their lives. 5 out of 6 times (reality is more like 50/50 though), they might get away with it. But when they don't, the fish have to suffer (and be stressed) with ich. I just don't think that is very responsible, IMO.

so you dont think that chasing a fish around a glass box with a net for a few minutes or for one minute several times in a couple weeks is stressfull to the fish?....I think you are vastly underestimating it, or perhaps are in denial about what we put our fish through....many game fish are hooked and released in less than a minute and still die from LA build up....how is that any different?....just cause there is no hook involved?