How long had they been in their previous tank? I'm assuming that the tank was well established.
Here's what I would do:
1) Go to Target. Get a cheap Sterilite storage tub, and a pair of nylon panty hose.
2) Hit up the local fish store:
- Marineland Aquarium Bacteria
- SeaChem prime
- API Water Test Kit (if you don't already have it).
2) Get home, rinse the tub, put in a 5x dose of SeaChem Prime, the pouch of Marineland bacteria, and then fill with water to stir.
3) Take the pantyhose from Target. Fill the two legs with the gravel, tie them off, and then cut them off to make two sacks of gravel.
4) Take everything from the old tank - any decor, the filter, bubbler if you use one, and your sacks of gravel - and move them to the Sterilite tub. (Personally...... I'd move a little bit of water too, just to give it the "smell of home" but I don't think there's any real benefit there... lol. I just get the gut feeling it'd make my fish's transition less stressful.)
5) Introduce the fishies to their new, temporary home, and test the water like there's no frickin tomorrow. I've seen the MarineLand Bacteria work wonders, but if not, you can save your fish by using the 5x dose of SeaChem Prime. Be prepared for a bunch of water changes...
Here's my reasoning:
The major danger in moving your fish to a new tank is the loss of bacteria... I tried to do an "instant cycle" by moving all my fish's stuff (where the bacteria lives) with him, so that the bacteria would come too, and it didn't work!
So I was dosing with 5x Seachem prime to keep things from being toxic, while still allowing there to be ammonia and nitrite present to encourage the bacteria populations to grow... It was SLOOOW going, especially because I couldn't stand to see the levels be high, so I was doing frequent frequent water changes! (Good for your fish, but makes bacteria colonies grow slower...) Adding Marineland Bacteria finally did the trick!!
Best of luck!
