My buddy is upgrading to a 125 at the moment. He is keeping mbuna, which are currently in a 55. He has the tank all setup, heaters, filters, and lighting. The water is the same temp as the 55 and dechlorinated. He asked me if he could just take out all 70 lbs of rock in there and all of the sand and even run the canister filter that's on the 55 on the new tank. He already has a ton of rock filling about a third of the new tank. After doing that, he would catch all of the fish and put them in the 125. I'm also genuinely interested in this question because if doing that replaces the need for fishless cycling, I have wasted countless weeks on doing a fishless cycle. It would also mean that I get a free 55 a lot faster lol. I asked him how long the transfer of the sand, rocks, and filter would take, and he said no more than 1 hour. I told him it might be a little stressful for the fish, but in terms of making the new tank ready for fish, it would probably do a great job, as it is pretty much the same amount of beneficial bacteria that was supporting the 55, except moved to a bigger tank. Am I wrong? I forgot to ask him, but I would assume water parameters are the same, save for nitrates, in both tanks as he doesn't mess with the tap water, except for dechlorinate it. I don't see any way of shocking the BB colony. Any help/advice would be appreciated.