I think it may also be the food. When I bought the tank from my co-worker, she threw in a small container of fish flakes. The container looks years old, so it'd probably be all stale and gross by now. I'm going to the store in a little while to buy some new food.
Also rearranged his tank while I was changing the water. Woke up this morning and found a tiny tear in one of his fins and I think it was the plants. I put A LOT of plants in there, so I ended up taking some out. He seems to like it a bit more.