Tank Upgrade - Kickstarting The Cycle ?

Hi fdm,
Are you transferring all your fish and leaving the old tank empty? If so option 3 is probably the way forward. (Although you may not need to bother transferring over the water)
The good bacteria are in the filter, not the water, and there's not much ammonia in a mature tank so transferring the water over won't do much.
If you are planning to run both tanks, follow sue's advice in the link you posted.
She will no doubt be on here later today to give more expert advice anyway.

What do you mean by 'no turning back?'

Given that you already have a tank running I would disregard option 1 - nothing wrong with this approach but it will take quite a while and it seems a shame not to take advantage of the tank you already have running.

Otherwise it may depend on how patient you are really! Option 3. should be the faster as you would effectively be just transferring a cycled 'tank' (i.e. bacteria in the filter) from one to the other. I would also transfer the water in this case because whilst most of the bacteria will exist in the filter, there will still be some bacteria on the contents of the tank and in the water. The subsequent addition of fresh water to fill the remainder of the larger tank shouldn't make any difference as the amount of waste being produced won't be changing. You would most likely lose some of the bacteria through the transfer process but it shouldn't make any significant difference and the bacteria will soon recover.

If you're a bit worried about the prospect of having no fall back and you're not in any rush then I'd go with Option 2. The way I would kick-start the cycle (this is what I did recently) would first be to do a decent water change from your existing tank (1/4 to 1/3) and put this in your new tank then top up with fresh (declorinated). Then take some of the media out of your existing filter and put it in the new filter (again about 1/4 to 1/3) and replace this using media out of the new filter. I would also then add some contents from the existing tank such as decorations (as these have a beneficial bio-film). You can then either do a fishless cycle using ammonia (which should be much quicker than starting from scratch) or potentially transfer a small amount of fish to start with (i.e. about 1/4 to 1/3 of your current stock) as the bacteria you've transferred should be able to cope with this amount, and then gradually add more fish over time whilst keeping a close eye on the tests. This might not be quite the ideal and/or most scientific approach but should work and allows you to keep the other tank as backup should the worst happen.

Thanks for the very helpful replies everyone!

So I think I'll go for option three since it allows me to enjoy the new tank much sooner

I'll get it set up, fill with new water and let it warm up overnight.
I'll then migrate everything over, including the old water.

I'm happy to run the U2 in conjunction for as long as it takes. I can switch it to deep irrigation mode anyway which will help with new plants that I want to put in.

I'll also remove one of the sponges ( replacing with a fresh one ) and chop it up for the new filter to help it out.

Soon ... more fishies!

Thanks again for the help, much appreciated!

FDM