Seems to me there have been a few threads lately extolling the virtues of a socialization box (some contributed by myself). I have also had a few folks ask me what I am using, so FWIW, here is my approach cobbled together over many years of personal experience and invaluable advice .....
There have been many threads on the acclimation process; and many steps. For better or worse, here's what I do:
With a few exception, which I shall note later, all new fish are placed in my socialization box - some as short as a single day, others for 2-3 days. Never longer than this though. Once aggression appears to have died down, I introduce the new fish just after the main lights go off. If subsequent aggression is still high, taping a mirror on one end of the tank is amazingly effective at keeping the alpha bully busy. Using this process, I have had a very high success rate with introducing new fish.
So, what is the socialization box .....

Essentially just a clear container that allows the new fish to see and be seen, but not interact. There are a few commercially available options available but, frankly, I just made my own. Once, because I am pretty handy, cheap and had materials on hand (all sunk costs); two, because my tank is large, I had plans to introduce groups of fish, and all of the commercial options were too small.
I used 1/4" clear acrylic for the sides and for the 'hanger'; 1/8" white acrylic for the bottom, and egg-crate for the ends. Inside, a piece of 2" PVC is glued to the bottom. There is room on the bottom for as small tray of sand in the event I am introducing a sand burrowing fish. Works very well except for really small fish that can swim through the egg-crate.
The only time I do not use this box is if the fish being introduced is very large and/or likely to be the alpha; or if it is very small and likely to hide in the rockwork for a while anyhow. I recently added a trio of chalk basslets and didn't bother with the box for that reason. They had been fattened up in QT, however, so now, five weeks later, I see all three out and about.
No process is perfect, but the approach outlined in this thread has worked well for me. I cannot remember the last time I lost a fish to the initial acclimation process (though I have had a few in-the-bag DoA); I also have not lost a fish to the introduction process in a long time (defined as not lasting a month). I do lose fish in QT, for various reasons - not eating, disease, cement-floor-surfing - but that's about it.
Most of the fish in my tank have been introduced with this approach (beyond the initial 10 or so that came with the tank bought on craigslist), and I am not particularly mindful of introduction order - it's just not all that practical.

Hope this is helpful!
There have been many threads on the acclimation process; and many steps. For better or worse, here's what I do:
- I quarantine all fish for at least 6 weeks, often 12.
- Initial introduction is accomplished by adjusting QT salinity to the shipping bag, and temperature floating for 15 mins. Incredibly easy on the fish and will reduce initial acclimation losses to near zero.
- I strongly advocate a simple ATO on all QT tanks, so bringing salinity back up to 1.025/6 is easily done over a period of a couple of weeks (also keeps med concentrations steady).
- QT is for disease prevention, certainly, but it is equally useful to get a new fish eating in an calm, non-competitive environment. It has been my experience that the subsequent successful introduction of fish into my active display is much more likely if the fish has built up some energy reserves. Malnourished fish don't survive.
- I keep a canister of biomedia on my main tank pre-seeded so that I can remove some as needed and immediately have a 'cycled' QT. You can run an un-cycled QT, but it doesn't work particularly well for me because I feed new fish in QT as many times per day as I can manage with my schedule - this ends up being 5 times on average, but sometimes as many as 10. Important to use the Seachem ammonia alert badge regardless.
With a few exception, which I shall note later, all new fish are placed in my socialization box - some as short as a single day, others for 2-3 days. Never longer than this though. Once aggression appears to have died down, I introduce the new fish just after the main lights go off. If subsequent aggression is still high, taping a mirror on one end of the tank is amazingly effective at keeping the alpha bully busy. Using this process, I have had a very high success rate with introducing new fish.
So, what is the socialization box .....

Essentially just a clear container that allows the new fish to see and be seen, but not interact. There are a few commercially available options available but, frankly, I just made my own. Once, because I am pretty handy, cheap and had materials on hand (all sunk costs); two, because my tank is large, I had plans to introduce groups of fish, and all of the commercial options were too small.
I used 1/4" clear acrylic for the sides and for the 'hanger'; 1/8" white acrylic for the bottom, and egg-crate for the ends. Inside, a piece of 2" PVC is glued to the bottom. There is room on the bottom for as small tray of sand in the event I am introducing a sand burrowing fish. Works very well except for really small fish that can swim through the egg-crate.
The only time I do not use this box is if the fish being introduced is very large and/or likely to be the alpha; or if it is very small and likely to hide in the rockwork for a while anyhow. I recently added a trio of chalk basslets and didn't bother with the box for that reason. They had been fattened up in QT, however, so now, five weeks later, I see all three out and about.
No process is perfect, but the approach outlined in this thread has worked well for me. I cannot remember the last time I lost a fish to the initial acclimation process (though I have had a few in-the-bag DoA); I also have not lost a fish to the introduction process in a long time (defined as not lasting a month). I do lose fish in QT, for various reasons - not eating, disease, cement-floor-surfing - but that's about it.
Most of the fish in my tank have been introduced with this approach (beyond the initial 10 or so that came with the tank bought on craigslist), and I am not particularly mindful of introduction order - it's just not all that practical.

Hope this is helpful!