So, I'm thinking of a Whisper 60 HOB, used in conjunction with my current Whisper 40 HOB. Theoretically, the 60 alone should be enough, but I'll combine it with the 40 to take into account rbishop's advice to consider the manufacturer's gph claims as over-estimates. And as southpaw says, I will find a way to get the 60 filter running on my 20 gal for at least 2 weeks prior to the upgrade. Now, I've read conflicting reports over what kind of cycle will happen with an upgrade. I recently downgraded to a 10 gal in order to give a new home to an old gourami who was getting picked on. I bought a new filter for the 10, cut the biological filter sponge in half, also cut the cycled bio filter sponge in my 20 gal in half, and switched the halves. I also put gravel, plants, and decorations from the 20 into the 10. I put the gourami in immediately. That was 2 weeks ago, and so far I've had no measurable cycling. Ammonia is 0 and stays there. If I do essentially the same thing when I upgrade to 55 (minus all the cutting sponges in half), will it be ok to move my fish immediately? I've read conflicting things online. The general consensus seems to be that if you set up your new tank with old gravel, old decorations, old plants, and established filters, then it's ok to move the fish at the same time, and just keep an eye on the water stats. But, while I've got this thread going, I'll go ahead and ask you guys for any advice or opinions on this. Thanks again!