Just a note, may not be as prevalent or big issue in fish tank plumbing, but be on the lookout. Look down any pipe you are working with, as I have found when finishing a 3/4 bathroom and moving and adding to a gas pipe bubblegum in copper tubing and a wadded up piece of paper in gas line I have purchased. It only takes a second to look, but could prevent some major headaches. Certainly a good 101 topic.