Overseas! Cool! Maybe you can be near the ocean and you won't need a tank!
Rykna, you bring up some very valid points. The rates of childhood disease (asthma esp) have been rising and a lot of immunologists are blaming it on our antibacterial soaps and handcleaners. Like you said, exposure makes us stronger.
About covering the tank, most of the pathogens (bacteria and viruses that can cause disease) in our terrestrial world cannot grow in saltwater. So, prevention of tank poisoning really is about things we can smell and see in the air. I don't cover my tank because of the gas exchange issue you state but if I am doing anything in the basement involving something stinky, I do!
I am kinda on the fence about quarantine. I agree with you that exposure to pathogens is vital to all my fish. I don't quarantine, but I can't recommend it to all. I really think most tanks, of those that do quarantine do get exposure though. People buy corals, and algae and add reefpods and phyto. All could have potential damaging organisms.
But, I have spend a long time researching and thinking and attempting to amplify my tanks immune system. All the things we are talking about fit into that. I'll bring up more. I do have an instant hospital "ICU" tank ready in the waiting, too. Interesting side note: I have heard of research for a vaccine for our pets, for the bacterium Vibrio. It is a common bacteria in our oceans so I am not sure how it will pan out, but we'll see? I am not sure how it will be administered though!
So, a few more things to consider in the environment category:
Biodiversity. When we set up our tanks, we usually buy our rock from one source. So, we get the crawly, the tiny and the weird bugs, worms and sponge that was in the reef where that rock was "grown". We all know that die off is huge during transport and curing. Then, the rock is transported out of the water, so we get more die off. If we can find a way to increase the organisms in our tank, we can have more diversity which might provide protection from certain elements. For instance, sponge is possibly a bacteria filter. Differing species of sponge in our rock might make the environment stronger?
I think that certain species compete with others, and some win, some lose. So, I add a small piece of rock every once in a while. And, buying a coral gets us the best live rock. It has been in the water all the time and has no die off!
I have been blessed with a few issues with this practice, though. I have had majanos, aiptasia and flatworms. But, now they are gone and I have some really funky sandbeds critters!
One more issue I can think of to come....