Enoid;1514500; said:Ignore the pleco, Just put some gravel from your 125 in a filter bag and put it in the Quarantine tank. I keep mine bare exept sponge filter, and bag of gravel.
More bad advice. The gravel will have some BB, but most of his BB will be in his filters (they have more flow, more oxygen and access to more food for the BB). Also, the BB in the gravel will die in a bare tank if left in it to keep it cycled, so there is no real benefit to it. If you want to keep the tanks seperate, to keep the tank cycled throw in some guppies or other disposable fish and cycle the quarantine tank. When you throw in the new fish, if the guppies die or get sick, so what? The tank is cycled and you don't lose your prize/expensive fish.
The best advice is what Ziggy said, keep a sponge filter in your main tank, use it on your quarantine tank when you need it, then sterilize it and throw it back into the main tank when the quarantine is done. You will need a heater (50 watt would be fine) for it. Bare bottom is best as you will need to dose correctly and gravel/decor will change the amount of water the tank is holding.