My tank has a sticker on it that says that it was made back in 1991. That is 15 years. I got mine used about 6 months ago and the person who had it just topped it off. Never cleaned it, and when she called me to ask if I wanted it, I said sure. She said "You will have to empty the water and bag the fish yourself.". I went over there and vacuumed the gravel as I removed the water. There was brown gunk coming out of the gravel. It had not been cleaned since the last time I was over there and cleaned it.....2 years ago!