Quarantine Tank, how to start one...

I think typically a quarantine tank is a 10g. 5g should be fine I think for smaller fish and such, but to be honest I paid $9 for a new 10g.

Yes, you will need a filter for a quarantine tank. The filter really depends upon what you want and what you have set up. I have a corner type filter with a airstone in it. It came with a funky little cartridge, but I pulled that out and made a type of sponge filter. The general idea for me is that I can take the sponge off of the intake to my cannister filter and just stick it into the quarantine tank when needed. Instant bacterial filtration from a ready source. I believe you had a 20g tank so you probably have a HOB type filter. Generally since a sponge filter for a 5g would be fairly small you could put it inside your HOB filter when not in use in your quarantine. I have 2 reasons for using a sponge filter in this case. One its relatively cheap. Two my quarantine tank can double as a nursery for fry if I ever have the need.

Ok, now if there are no fish in the tank yes the cycle will be blown all to heck. I mean you could keep the cycle going if you really wanted to, but you also have to ask yourself why.

Generally speaking you don't need to transfer any water from main tank to quarantine. The bacteria you would want is a surface type and doesn't last long in the water column. I have transfered an ornament from my main tank to the quarantine to transfer bacteria that way. Another thing I will use in a quarantine is anacharis. I either clip some from my tank or just buy some at a LFS since its cheap and float it in the tank. It's getting late so I may be rambling.

http://www.aaquaria.com/aquasource/isolation.shtml

But in short, whatever size tanks suits your needs is suiable for QT.

Keepining a small internal or extrenal flter operating on another tank will maintain the needed bacteria in the filter ready for use as needed.

Nice link.

I've been wondering something about QT's myself. I have a spare 10 gallon tank that I use for partial water changes as well as two filters on my display tank(1 of them is a small power filter that is very easy to move).

So, if I ever need a QT I could just fill up that tank with some water out of my main tank(So its already the right temp and dechlorinated), switch the power filter over, put in one of my extra heaters, and presto!

Instant QT, no?

Watcher - yup - that is the good and easy way. I'm all for simpifying my life.

My display tank is only a 29 gallon(got all my tanks from a friend who can't keep doing aquaria. I'll get a bigger one eventually.). So I have a extra 10 gallon that I've always used for partial water changes.

10 gallon tanks are cheap. I've seen them for $9. If you made sure to keep some water in a bucket somewhere so it's dechlorinated(or use additives to get rid of chloramine) then you could throw that in a 10 gallon and heat it up pretty quickly. Within a few hours or so.

If not, then a 5 gallon is around the same price as a 10 gallon.