I'm planning on setting up my first ever aquarium, using fishless cycling. When the tank has cycled I will put my first fish in. Over time I will add more fish, which I will put in a quarantine tank first.
I know a lot of people only set up a quarantine tank as and when it is needed, and keep the filter media for it in their main tank. If I do this with a new tank with only a few fish, would there be sufficient bacteria or would I need to do a fishless cycle for the quarantine tank as well?
If you keep the QT filter running in the main tank, you won't need to carry out a fishless cycle, no. However, to save a little on your electricity bill, you could also just keep the media (the stuff inside the filter) in the main filter and take some out when you're ready to get your second lot of fish.
Assuming the main tank is fully cycled, when the 1st fish go in, you'll get some die-back to accomodate the new bioload. Once you take some media out for the QT tank, the bacterial population will respond and will soon catch up.
If you're worried, just keep an eye on ammonia and nitrite levels in both tanks for a few days
Skulk wrote: I was worried that there wouldn't be sufficient bacteria for the QT filter, and not enough left for the filter in the DT.
That's why I suggested keeping an eye on ammonia and nitrite for a few days after getting the second batch of fish
Would it be necessary to do greater and/or more frequent water changes while the bacterial population catches up, or is there some margin for error?
It would only be necessary to carry out additional water changes in either/both tanks if you find an ammonia/nitrite spike. If ammonia and nitrite remain 0ppm, all you'd have to do is carry out the weekly water changes as per normal.
It occurred to me that once the DT had cycled, I could move the QT filter into the QT and maintain the bacteria with ammonia until I'm ready to get more fish.
Of course you could. Just as long as you keep the filter "fed" with a supply of ammonia every day.
At the end of the day, it's entirely up to you whether to cycle the QT filter independently of the main tank/filter, but having "borrowed" some media from my main tank for my own QT, I can honestly say I've never experienced any problem with ammonia or nitrite. Of course, the first time I used some of the media, I was nervous in case it didn't work, but I needn't have been. The bacteria are already there - it's not like they have to start from scratch again, so they recover their populations quicker than bacteria establishing a new territory in an unclyced filter.
You could do that yes if you're willing to. As for additional water change - it's best in any situation where you've either increased stock or reduced the bacterial poulation by removing media to monitor ammonia and nitrite for a few days. If they stay at 0 there's no need to change your routine, but if you get a spike on either, extra water changes will be needed until it settles.