The gravel is colonized by bacteria, but typically not in particularly high numbers, so changing the gravel should have a minor affect. You're best to keep an eye on levels of amminia/ nitrite after, just in case, but it really should be fine. If you're worried, try putting the old gravel in the foot of an old (but clean!) pair of tights /stockings and putting it in the tank for a couple of weeks, until bacteria have colonised the new gravel.
I'd use 50% old water and 50% new water, making sure that the new water matches the temp/ etc of the old water as closely as possible, and adding it slowly.
I'd say you need to use some of the old medium in the new tank to get it to cycle quickest, because how else are you going to transfer the bacteria from old filter media to new filter media?
I'd use 50% old water and 50% new water, making sure that the new water matches the temp/ etc of the old water as closely as possible, and adding it slowly.
I'd say you need to use some of the old medium in the new tank to get it to cycle quickest, because how else are you going to transfer the bacteria from old filter media to new filter media?
