25 fish in a 20g tank is yes over-stocked. The Forza FZ9 Canister Filter keeps the Ammonia and Nitrites at 0, but the Nitrate levels become high very quickly and 50% water change and gravel cleaning MUST be done weekly. Seachem Prime can detoxify the Nitrates, but I do not rely on it, and special resins in the canister filter also help get rid of Nitrates, but these resins are expensive and eventually stop working and need to be replaced. The tank is heavily planted with driftwood allowing plenty of places to rest. My tank is in my bedroom and I like watching it just as much as watching tv and movies. I'm happy and appreciative that this site exists and so many people are there to help each other.