I just recently experienced my 1st real tank crash. I have a 55 reef that was going really great. The wife decided that she wanted a nudibranch, and I didn't feel like arguing so I let her get it. She was already mad because I told her that we didn't need a fire shrimp. Anyways the nudibranch managed to onto the intake to a powerhead, it did have a prefilter, and it just got stuck. Didn't notice this until the next morning, and by then the tank was pretty cloudy. I was ticked, and about to throw everything out the door. The next few days I lost a frogspawn, closed brain, candy cane, gonopora, buble, lots of mushrooms, and all my cleaner shrimp & snails. Somehow my elegance, xenia, polyps, another frogspawn, and a few mushrooms survived.