i used to use a small container in the tank to acclimate similar fish together. it works great. keeps the fish from fighting, get's them used to seeing them. doesn't take long for them to accept their new neighbors.
i used this. it was also my DIY fish trap. it is just a little beta tank with holes in it to allow water flow. i helped a friend pair up a male and female angel fish. this is how i introduce new tangs as well. 3 days of slashing at this plastic container, and that's it. no fighting when the new guy gets let out. no injuries sustained by any fish. i highly recommend it. you can make a bigger one. i can't find a pic right now, but in my large system i had a 10g size acclimation container.
jon