Hello; I used a 10 gallon tank as a QT for a number of years. I have used other sizes, basically what was on hand that did not leak and would fit on the bottom shelf of my metal tank stand. A QT has to be set up much like any other tank in that it needs to have a population of beneficial bacteria (bb), a heater, and some sort of filtration/aeration. I usually have a full lighted hood nowadays but have used a pane of glass as a cover in the past. For filtration/aeration I have used a bubble powered sponge filter, a small hang on back filter and sometimes just a bubbler.
The sponge filter is handy as it can be in a disply tank and become colonized with bb, then stuck into the QT so that the QT can be ready to recieve fish quickly. I copied a forum suggestion and got some foam from Wal-Mart and cut it to have two sections of foam on the sponge filter. This way I have two bb loaded foam sections to throw into a new setup to speed up the cycle.
I usually do not put substrate in a QT, just a bare bottom. A clay pot or some stacked pieces of slate go in for any new fish that need a hiding place. This stuff can be quickly removed and cleaned when necessary.
I usually keep a QT filled and filtered all the time. I keep some snails and non rooted floating plants like hornwort in it. I sometimes keep at least one fish in it all the time. This keeps the tank going and ready to recieve new fish or become a hospital tank.
The size of the QT will determine how many new fish can be kept in it during the quarantine peroid. The fact that a very small tank is basically harder to maintain makes me tend to use the largest tank available. I would probably not go below a five gallon at any rate, but a smaller could be used. A QT has the same needs as any other and the small tanks can go bad very quickly.
One accidental discovery made some years ago yielded a nice bonus. I would siphon water from the QT for a water change to be discarded. For reasons that i do not recall, I started filling the QT with tank water from a display tank on the stand above it. (I was not keeping any fish in the QT at the time.) I would usually get a cup or two of gravel thru the siphon into the QT. I left it there and replaced the gravel in the display with a supply of cleaned gravel. I then filled the display tank with fresh water. After doing this for some weeks I noticed fry in the QT. I had siphoned fertile eggs into the QT and they hatched. Over the years i got a few bonus fry this way.
I am finishing up new drywall in the corner of the room where my tanks are and do not have a QT right now. I hope to finish up soon. I need to change out a standard wall outlet for a GFI that was hidden behind the tank. I have been down to only one tank set up for a while. I want some new fish and have gotten to the point of not getting any without a QT. Better to wait than infect my display tank.
