Upgrading 20 To 55

I'm upgrading my 20L to a 55. Current inhabitants: 1 panda Cory (There were more, but only one survived more than 24 hours after arrival from the LFS, and I'm waiting to try again til after the move), 5 green Cory's, 2 Murray's River rainbow fish, and a small school (7?) of black neons.

The old tank has gravel; new one will have aquarium sand. New tank will use the larger of my two existing filter from the 20 plus a new AC 70. After several weeks I'll replace the original filter with another new one - so the 55 will have one filter on each side of the tank.

Also will be moving over the plants.

I'm trying to figure out the steps involved. I will have the sand in the new tank by tomorrow (new tank is in a different spot than existing). Do I set up the new tank like brand new and let it cycle? How long will that take since I'm using my existing filter? Or do I move over the filter from the 20, move over half the water from the 20, fill the rest with conditioned water, check water parameters, and move the fish in right away? I've read several threads but I'm still not sure the best way to go about this.

 

This might help..

 

Thanks. I wasn't sure if things are different when not transferring over the substrate, since so much of the BB lives there -

 

The vast majority of the bacteria lives in the filter media rather than the substrate. Just move the old filter over at the same time as the fish and leave it running alongside the new one for as long as possible.

 

Ok - I have the new tank set up (sand in, water added and dechlorinated, old and new filters running, some decorations and plants moved). But I just tested the ph in both tanks and it's a problem. I'm using an API liquid test kit (3 month old kit). The old tank tests at a ph of 6.0; the new tank at 7.6. They are using water from the same source. What would create such a substantial difference in ph? And is there a solution besides time to fix it? The old is 20G, so I can move over some water, but not enough to come close to filling the 55.

The actual tap water (directly from the sink) tests at a slightly lighter shade of blue than the 7.6 on the API chart. So something in the old tank is drastically lowering the PH. Maybe the plants?