Finally have a QT...
I found this in an old post and since I have a small 29 gallon and a 6 gallon, I know that I'm not going to be adding a lot of livestock and things to my DT often, so I thought that this post is the way to go for me. But since it's an old post, have things changed...
A ten gallon tank, power head with sponge filter, heater (small), air pump and stone ( again small) , also a 3 or 4 inch round pcv pipe, I like to get the T fittings in that size at Home Depot (for hiding). run the power head with sponge filter in your main tank for two weeks. when you do your regular water change then use the old water and fill the Q tank and transfer your power head to the Q tank as well.
When you get your new fish in the Q tank you will need to monitor the ammonia levels every day and change ten % of your water as needed. the sponge filter will have some bacteria on it to break down ammonia, but you will still have to watch for increases.
The tank that I have for QT was given to me today. I don't know the Gallon Size but the measurements are 24" x 16.5" x 12".