Luckily, this is super simple. Just move your rock along with the livestock to the new tank on moving day.
As noted here, the biological filter resides in the rock.... ergo, you're simply moving the filter with the other livestock. No need for additional biological capacity as it is sufficient for your current bioload. The increased capacity of the tank, via additional gallons, has no negative impact. In fact, it provides you with extra margin via dilution of any wastes.
As noted here, the biological filter resides in the rock.... ergo, you're simply moving the filter with the other livestock. No need for additional biological capacity as it is sufficient for your current bioload. The increased capacity of the tank, via additional gallons, has no negative impact. In fact, it provides you with extra margin via dilution of any wastes.