What does cycling mean?

[fishdude]

how do you do cycling and what does it mean?

 

[reg2k2]

Fish create waste, which breaks down to ammonia. Bacteria then form to break the ammonia down to nitrites and then nitrates. These bacteria become biological filtration for the tank. Ammonia, nitrites (nitrates,too, but less so) are dangerous to your fish.

You can cycle w/fish or do a 'fishless cycle'. Kinda lengthy, but I think this thread covered it pretty well.