The last used tank I bought was a 65 gallon that was at one point a reef. All the ballast were fried, she had put two shop fluorescent bulbs over the tank, one was blown. All the inverts were dead, she didn't clean them out. There was a full grown maroon clown still in it, alive somehow. She hadn't done a water change in well over a year, and the tank stunk horribly. There was SO much waste in/on the rocks when we took them out the water looked like a swamp. The waste was easily an inch thick on top of the CC substrate. Got home, tested the water while it was still in the buckets, nitrates maxed out the api test which is 160ppm. I sold the maroon to my LFS
and dumped all the water. Threw out the lights and started completely from scratch. It was so NASTY. She said she didn't enjoy keeping them anymore, so I asked why she didn't sell the system the moment she decided that. Not only would the livestock gone to a good home, but she would have gotten some decent money out of it. I only paid 300, for rock and all. It was a nice tank once I fixed it up, I sold it for 500 a few weeks ago.