How do I cut the TOP yellow part of my lucky bamboo?

Why did my lucky bamboo plant turn yellow and mushy?!?

• My lucky bamboo plant was long and had a bunch of leaves it was turning yellow and next thing i noticed it was dieing. Well only the part out of water, it was yellow skinny mushy and had some black parts. so i cut it off up to the healty green part ,it has no soil just water and rocks it has alot of healthy looking roots but i still want to know why it did that. 10 pts to the person with the best answer!

• Answer:

  You must have either not given it enough water or moved it to another environment that it did not like. Note bamboo plants can also die from age, they don't usually live past a year or so.