Hey peeps! Earlier this week I bought a 55 gallon aquarium off Craigslist. When I went to go pick it up the owner was draining it and placing all the accessories in a box (the tank came with all the lighting, stand, filter, heater, etc). I brought the tank home and immediately set it up. I rinsed out all the gravel, decorations, and accessories, as well as the inside of the tank (except for the filter) and started her up. The tank is now running with everything that was originally in it, plus the filter with some original tank water (I did NOT dump the water that was left in the filter thinking that it could help 'seed' the tank) and it's original filter cartridge. My question is, do you think this tank needs to be cycled since it was already being used before I bought it? There's no way to tell if there was fish in the tank right before he sold it, the only reason he gave for getting rid of the tank is that he has had it for 15+ years and his wife is sick of it. There was a good amount of alge built up on the sides of the tank and on some of the decorations, so my guess is that the tank was at least 'biologically' active. I should also mention that while I was cleaning out some of the decorations, I found a half eaten pleco body wedged in between some rocks. It appeared to be relatively 'fresh' as gross as that seems. I ordered and API master test kit and it should be here later this week to tell for sure, but what do you guys think? Does this tank need to be cycled given that it virtually had a 100% water change? Thanks in advance!