I had a saltwater tank years ago and didn't really know how to take care of it. I took it down and put the live rock in a bucket. Now that I have a saltwater tank again, Will the live rock come back alive?
Yes, the rock itself isn't lve. The bacteria on it is though. Although it is baron right now. Imagine it like a house. When people are living there, it is live. When they move it is dead. A vacant house will only be vacant so long. So once you put it in your tank, new tennants will start moving in and it won't be dead. But this could take a long time, couple months before it is fully Live Rock.
One rule of thumb on bas to live rock is 12 months. It can take 12 months for it to be fully live again. I'd say good results are achieved in more like 6, but then it's just the surface layers, not necessarily everything.