@Jay Hemdal I lub ya and I REALLY appreciate your insight, but I completely disagree with you here. Kamakazeee.
Everyone on this thread is going to be pro QT. I doubt there will be any dissent but me, and I will probably come to regret going against the orthodoxy once again. Here goes.
No QT means two things in people's minds. First I don't care and I just threw my fish in. This is what I will be smeared for. The second way which I actually practice is more thoughtful, but will be morphed into something I taken out of context, like a game of telephone.
This discussion is born of a base thinking. The two viewpoints on that thinking are maintain a sterile environment that only the things that I approve of enter or it's counter point is that the ocean is messy and I should look for biological competition and diversity. This is not to say that the two viewpoints don't have overlap in fact they do and that IMO is where the real discussion can take place.
Most people are aware of the sterile thinking, in fact at some level most have it. Even people that say they don't use QT. I used to have it so I get what is being said. I am not going to re-hash it here because I think it is well worn. Please do not say that I don't understand because I do, like I have said I have lived it and what I found over my 35 years of this is that it is less successful than a more natural approach.
I am going to speak to my approach because I don't want to put words or thoughts in the mouths or minds of other natural advocates, but I will say that many many many of the ideas that I use are rooted in the same thinking as those people.
First off no QT for me does not mean do nothing. That is entirely incorrect and I don't like being smeared with it. I have suggested many times to people having trouble to implement some of the ideas that I am using and they tell me that it is too hard and they aren't interested. Unfortunately they then go to a QT method to face a new set of challenges. THERE IS NO EASY WAY out of this!!!!!!!!
1. Gas exchange gas exchange gas exchange. This was the first thing that I observed to be key to no QT. I got this idea ultimately from my time in the Philippines. Here is what I saw on the "reef"
Guesses as to how many GPH this is? Mine is a lot, and I have gone with that. Over the years I have perfected how to get massive turn over without blowing everything around. You can see my build thread for what I have done if you are curious. My thought for the aquariums is huge surface agitation and surface skimming through overflows. This creates the best situation I have been able to come up with to ensure the air outside of the aquarium is in equilibrium. I would like to say use protein skimmers because their gas exchange is huge but they do other things that I don't like and that out weighs their awesome gas exchange.
Addendum to gas exchange is something that I have come to recently understand. It first came with the idea of ph being depressed from household CO2. I finally tested my household CO2 and I just about dropped dead with the amount of CO2 that is in the house. Once again you can see my build thread for the numbers and the solution. My conclusion was that if the household CO2 was high from the two humans in it, wouldn't it make sense that the O2 would be depressed? I went with this theory. I believe it is solid, and dovetails into my massive oxygen requirements.
Why I think elevated O2 is important for successful non-QT, or more importantly a successful aquarium. First off oxygen affects metabolism. Metabolism drives immune response. If you are being slowly suffocated it is hard for your body to fight infection, it is more concerned with basic function. I don't think most collectors distributors care about gas exchange because it adds capital costs that are hard to recoup. Second along the same lines, digestion is a huge consumer of resources in almost any creature. Lowered oxygen impedes digestive function at time that is most critical for the creature. Lastly most parasites are going to target the gills of fish. Because this is where the nutrients and fuel are at. This further impedes the fishes ability to uptake oxygen which affects the other two items. All of this creates a negatively reinforced spiral.
Next up in my thinking on non-QT is biological. This is a two part approach. The first thought is that active predation of parasites that fall off of the fish in a biodiverse tank helps limit the amount to re-infect. The goal isn't elimination the goal is load reduction. Leaving the parasite present but under-performing, which segues nicely into the next part that I have taken from
@Paul B. That is inoculation through constant low level infection. This ensures that when a new fish with a high parasitic load is introduced to the tank the fish that are currently in the tank are most likely immune and can easily deal with the infection. I am aware of things that don't have free swimming stages are unaffected but that is where I fall back on gas exchange.
Finally meds. Medication has consequences both to the fish and the biome that they are introduced into. I think we are all aware of the biome problems, there are thoughts on how to deal with that, but little regard is taken on the damage done to the fish. We don't yet seem to have a good way to try to mitigate the effects the meds on the fish. IME the meds hit the fishes digestive tract ... HARD. This is the worst because most fish have endured lengthy transit as
@Jay Hemdal pointed out. They usually don't eat and are medicated the entire trip. This means their reserves are depleted and just when they need food the most they can't process it. I believe that it can be so bad that as soon as the fish eats it's system will shut down and it will die.
Fish eat anything, why are they so picky in our tanks. I have vomited in seawater and fish came from seemingly nowhere to chow down. My wife as feed fish cheerios to get them to come out. My dormate in the Philippines would feed his net collected fish Tetra freshwater flake. All of this, and more, for me point to something being wrong with the fishes food intake when they arrive at our aquariums. I believe more specifically their digestion.
These are the two core prongs of my view of a non-QTed system, gas exchange and biodiversity. Also why eschew meds. I am not against them I just believe that there are cons and they should be weighed against the pros before being used. Too many are either unaware or nonchalant about the cons, and I find this infuriating. Are there exceptions in all of this ... of course yes as in any approach. I am not per se against the sterility thinking and the QT that comes with it, but what I have found in my time and experience is that that thinking produces fragile systems that are prone to crash. Will all QT'ed systems crash, I don't know, but my experience tells me that this is the case.
FWIW