I prefer to run a small biofarm to keep cycled filter in/on so I can set up a tank and make it nitrogen safe right away.
There are basically 2 approaches one can take to Q (and Hospital) tanks. Once is to have a permanently set up tank for this or set one up as needed. I prefer the latter approcah for a few reasons.
First, the purpose of a Q tank is to catch amy potential problems in it rather than have them occur in the main tank. When they do, we respond by treating the fish appropriately or at least as well as we can. Diagnosing many fish ailments is not easy. Often we are giving it out best guess because we are not really certain what the problem might be. So when we have problems, we may or may not know what the cause is and we may or may not treat it successfully. The problems are when we fail in this effort and lose the fish.
In such cases it matter whether one's tank is intended to be going all the time or its a temporary tank. If one has a fully functional tank where the fish have all died and we do not know why, how can we know what is needed to insure the tank is safe once again? So the only option is to sterilize or destroy much of what is in the tank. We can bleach rocks, the hardware and even many plants. But we can not save the good bacteria. So we must throw out the media, many of the plants and perhaps any wood as well.
On the other hand if one has a tank with rocks, fake plants and a cycled sponge filter, when faced with the situation above, all we might lose is the cycled sponge.We can sterilize everything else involved and safely reuse it down the road. This approach is even more important in a hospital tank. Fish going into a Q tank may or may not have issues, but fish going into and H tank we know are sick in some way.
There is one other consideration here as well. Some of the cures we may have to employ can kill off the bacteria we need. When this is the case, we will be trashing the bio-filter. So for my part I never bother with cycling considerations in an H tank. I rely on water changes done every day or every other day at most. This method is not normally useful for Q tanks since, in my case, Q lasts between 1 and 3 months depending on the fish and from where it came. And these time periods assume I have no issues. Any treatment wfor anything resets the timer to 0 once the fish have been "cured".
What approach people use depends on their specific situation. The most important consideration in how you deal with either a Q or an H tank is what you do when the fish do not make it and you are not 100% certain of why they died. It is a lot easier for hobbyists like Byron or myself who have a fair number of established tanks and usually a few empty spares as well to manage using a Q tank. This gives us a lot of options. For people with one or two tanks, the choices are not the same.
No matter what system one develops for doing Q, the most important consideration is to be quarantining in the first place, Until you have wiped out a tank full of fish you have had for some time, you will not appreciate the benefits of and need for quarantining new fish. I have a number of fish now that i have had for over 10 years, I know I would be miserable if I lost any of them because I failed to Q new fish going in with them.
