Hello; I agree with most of the above. keep the old bb (beneficial bacteria) loaded equipment wet and try to not take too long to get the change done.
Hello; While I agree there will be some bb on the substrate, I do not think it is worth it to use old substrate as is in a new tank setup. I always either use "fresh" substrate or new substrate. By fresh I mean substrate that has been cleaned. While old substrate can have some of a tanks total bb population it will also be loaded with tank trash (mulm, detritus). To me the advantaged of the number of bb moved into a new tank is more than negatively offset by all that detritus. Sort of like taking a shower and putting your dirty underwear back on.
Bear in mind there is also some sessile ( I like that term) bb colonies on the glass of the old tank that cannot be transferred as well. So some steps can be taken when doing a new setup and using old bb loaded equipment from an established tank.
One is to not feed the fish in the new tank setup for a few days. This will slightly reduce the metabolic waste products (ammonia and such) from the fish.
I always get the live plants in a new setup right away. It is not so critical to have the new water temp as close as for fish. I also like to get the lights and filters checked out without the fish in the new tank.
Odds are you will not have the exact balance between bb population and tank bio-load in the new setup. With luck the balance will be close. The bb are slow reproducers so it can take a day or so for a balance to establish. You may have a slight ammonia spike but it should be short term. If you have a couple of weeks before the change you can increase the odds in a couple of ways.
One is to run some extra sponge filters in the old tank and allow them to become populated with bb.
If you feel compelled to try to get some bb from the old substrate then at least try to clean off some of the detritus. Put some in old tank water an give it a good swish or two. If you then decide you want all that junk in a new setup then go for it. That the bb are sessile means they will stick to the substrate surface and you will not lose all with some cleaning in old tank water.
I however use a garden hose and a stick (an old broom handle with the rounded end) to clean my substrate. I rinse about a half gallon of substrate at a time with the hose, then stir with a stick and pour off the nasty water. Repeat until clean enough. I figure to lose much of the bb due to the chlorine in my tap water but like clean substrate in a new set up.
Good luck
