I'm going to point out a few things here.
I disagree. Most people are unable to QT in a cycled environment unless they have multiple tanks at their disposal and a lot of equipment. Also, a full cycle is usually at its best when the BB has objects to cling to, things that are hard or unwise to have in the tank if you are medicating fish. Most of the QT containers I have seen have little to nothing in them.
Extra tanks are a dime a dozen. All it takes is a quick look on Craigslist to find some extra 10 or even 40 gal tanks laying around. And as you said before, it doesn't have to be a fish tank that you QT fish in. I personally use large tubs. Those are much easier to store. I even use them to hold fishkeeping equipment when they aren't QTing fish.
Now to your comment about having nothing in a QT tank; this is a terrible idea. Leaving a fish in the open causes stress. Fish, especially small ones like objects to hide behind because it makes them feel safe from predators, real and imagined. A bare tank is not a QT tank. It is not doing what a QT tank should: make the fish comfortable in its new home. De-stress the fish and it will take care of a lot of issues itself. They have pretty good immune systems when they aren't being compromised by stresses of an improper environment.
Also, many people find it either impossible or impractical to QT fish in a container that is actually large enough to even have a cycle. Unless you have a 5+ gallon you can't really do a cycle.
This may be true for a betta, but this doesn't hold true for any
other fish. This includes shoalers like tetra. They actually need a lot more room than most people think.
If anything, your fish are more likely to get sick and display signs of illness in an uncycled environment. It seems to me that having perfect water params is more likely to hide an illness a fish may carry.
Yes, fish are more likely to get sick in an uncycled tank, but the purpose of QT isn't to bring out the illnesses in fish. It is to heal any that arise. In a good QT fish don't get sick. They are de-stressed enough to heal themselves. I think it would do you good to read this article on stress and fish: http://www.tropicalfishkeeping.com/f...um-fish-98852/
I have rarely heard of people who are able to do cycled QTs, and I stand by what I said about not being able to cycle a tank in 24 hours. Unless you have a fully planted tank, this seems impossible. Mods, correct me if I am wrong.
As jaysee and Tolak said, if you bring over enough media it will cycle the tank. I have done this personally a handful of times. Never had an ammonia spike and all the fish made it through perfectly fine. I've even had gourami spawn in my QT tanks.
I was able to QT some of my sorority in cycled environments and their behavior in the permanent tank is radically different than it was in quarantine. I feel that physical signs of illness is a far better indication of their health (except for obvious lethargy or very strange behavior) than behavior.
Could this be from the stress that is living in a sorority tank? That is not a low-stress environment. What you saw in a less-stress QT was how they should act and what you are seeing now is how they act under stress.
Because the original question was in context of a very specific forum, I am not incorrect by my response that is applicable to that context, --snip--.
Yes. It is a betta forum, but these are NOT betta fish that we are talking about. We talking here as if this were a regular fishkeeping forum. This is the advice I would give to ANY fishkeeper getting tetras regardless of whether or not they also keep bettas. The fact that this is a regular fishkeeping subforum on a betta forum is irrelevant.
I would like to end by saying that MOST fishkeepers I know QT rather strictly. A lot of us have been bitten in the butt by not doing so. We are only passing on our recommendations based on our (sometimes very extensive) experience.
In this case I would just use a 5 gal tank or a 20 gal tub. Clone the media, and let them stay in the tank for a month. Maybe more if the fish in the tanks look sick. Floating plants whether real or fake will be greatly appreciate, and you can add mirrors to the tank to give the shoalers the appearance of a complete shoal. I've used this trick before, and it works wonders.