I want to address this too. There are levels of QT. One level is to not QT.
The middle is to observation QT for several weeks and only treat when you see disease. Lots of people do this one, but keep in mind it does not eliminate ich. Just because you don’t see signs of an ich outbreak doesn’t mean it’s not there and can show up later in your DT. Also, you might miss something. When I first started I had a fish with frayed fins. I figured it was bacterial or damage from fighting. Nope, it was flukes and killed at least 3-4 fish. So to do this right you also have to become an expert at recognizing disease and fish behaviors.
Higher level QT would be to treat for 30 days with copper. Treat for other parasites also (flukes, worms, etc. with prazipro) if you want, or only if you see signs, your choice. Then put the fish in your DT. This is pretty good. Also see number 3 below.
Extreme QT is complete and total ich eradication; making sure your tank is completely free of ich. This is what I do, and requires 2-3 QT tanks as below.
1) A mini reef tank for all corals and inverts for 76 days (or 6 weeks if the temp is kept >80.6F). This is because any of those creatures could have ich cysts that can release free swimmers (the ich can’t infect them, but can be on them basically). Everything added needs to be in that long, but adding new things doesn’t reset the clock, just give the finished ones a rinse in DT water and then add them (to remove any free swimmers from newly added things). You could instead buy all your corals and inverts from good sources where they’re kept in fish-free tanks. However, you’re also banking on the fact that where that reseller got them from was a fish-free tank also or that they’ve spent a total of 76 days out of whatever fish water (like the ocean) they came from. However, the overall risk is much lower if you do that. This has other benefits too; coral QT is good to do. It’s much easier to deal with coral pests in a QT system than your DT. I once had an order of snails bring in Montipora eating nudibranchs.
2) A fish QT where you treat with copper at therapeutic levels for 30 days. It’s a little risky to combine copper with prazipro because bacterial blooms can decrease oxygen levels so if you do, you’ll need lots of surface agitation and an air stone is a good idea. But, you also can’t lower the copper level in this tank to do it because the tank can still be infected after 30 days, see number 3.
3) A fish copper-free observation tank where you move them after 30 days for at least 2 weeks. During this time you can treat with prazipro to eliminate the other things. This tank is needed to observe because you can’t lower the copper in tank 2 after 30 days to observe or the fish can be re-infected by cysts that dropped off of them. The 30 days just eliminates all free swimmers not the cysts that drop off, and those cysts can still release free swimmers up to 76 days. And you definitely don’t want to keep a fish in copper any longer than necessary, it’s more toxic to ich and velvet than fish, but it’s still toxic. The purpose of the observation is to ensure no copper-suppressed diseases come back.
So that’s kind of the range of QT you’ll see people advocate for on here. Each level is associated with different risks and benefits. Both from diseases things can have, but also from the QT process itself as mentioned above. What you do is personal choice based on your risk tolerance. It just requires reading a lot about what those risks are, understanding parasite life cycles, figuring out how much space you have and what your significant other will tolerate, and the level of work you’re willing to put into the hobby. Some people advocate for no QT. And many more are happy with an
ich management approach and not trying to eliminate ich entirely. It’s up to you.