Need quick answer.. about to buy a new tank..

yes that will be good enough. Put your old gravel and filter on your new tank far acouple days and then stick fish in it. This is how lots of people cycle their tanks, myself included. It's just so much faster.

yeah that'll work. It might also help a little to add some of your old tank water. Not sure how much this helps, but it's can't do any harm.

The only thing you need to wait for in the new aquarium is for the water to get dechlorinated and aerated a little while. Use some tetra Aquasafe and throw in a bubble wand for a few hours.

Then transfer over the old filter and the fishies.

Can you do that at least?

the fish themselves don't nee the bacteria from your old tank it is actually the water.

Vato, didn't we already cover this?

The only thing the fish need is for the new water to have the same PH/KH/GH/temp as the old water. They also need it dechlorinated and to have dissolved oxygen in it. Nothing else is vital, though your tank might have a bacterial bloom for a little while, but that will not hurt your fish. Just wait it out.

They DO need the bacteria from the old filter. It will be best to put the old filter on the new tank. If not that, then at least the biological media from the old filter.

The fish do need the bacteria from the old tank, else the new tank will begin a new cycle. Transferring over the filter will be a big help -- transferring some gravel would help, too. Moving over some of the tank water might reduce the fishes' stress, but it is not critical. The tank water is the least important part of this equation.

No need to wait after you transfer the gravel and filter over, and get the filter running. If you use a water conditioner (Tetra Aquasafe is good, I use Jungle Start Right -- it doesn't matter as long as it takes care of chlorine AND chloramine), the dechlorination happens very quickly -- for our intents and purposes, instantly. You do not need a bubble wand to dechlorinate when a water conditioner is used.

To sum up, here's what I would do:

1. Transfer gravel over from old tank.
2. Partially fill new tank with treated tap water.
3. Transfer filter from old tank, get it running.
4. Top off new tank with old tank water.
5. Transfer fishes carefully (use a water bucket rather than a net if you can -- since you are transferring old tank water over anyway, this shouldn't be a problem).

Good luck -- do you mind if I ask why the extra 18 gallons are such an emergency?

Edit: To answer your second question, the Emperor 400 should be fine for a 55G, but it is always good to have extra filtration, so if the 280 is just sitting around, it wouldn't hurt to get it running alongside the 400.

TPIRman,

I only suggested the bubble wand due to the fact that water out of the tap is high in CO2 and low in Oxygen. I know that it is not needed for dechlorination.

As for using water from the old tank to top off the new tank:

Why do that if the water parameters match? You're just adding nasty, old tank water. Many breeders do 100% water changes on a daily basis to provide the best possible water conditions. And occasional partial water changes of >80% is a recommended way to prevent drifting water parameters and Old Tank Syndrome.

What I'm trying to say is that the fish themselves for their own needs for survival do not need the bacteria. They need the water parameters to be the same as their old water. But the bacteria is for the water so it does not go into an new cycle, there fore the rise of ammonia, etc. That would be harmful for the fish, but the the lack of bacteria itself is not what is harmful to the fishes health. What I am saying is that the new tank needs the filter and gravel to provide adiquate bacterial culture. The water from the old tank to the new tank is so that the fish do not go into shock because their parameters are so different, as the water itself does not have much benificial bacteria just floating around in it. I hope this clears what I'm saying up. I have learned my leason about cycling(watcher knows what I'm talking about) but I think I was a little vauge in this case, sorry for the confusion.