Hello! So excited to be a new member of Fishlore. I've had a 25 gallon tank for 2 years. I have 4 black skirt tetras, 3 mollies, a cory catfish, and a gourami. As I said, I've had this tank for 2 years, but I'm still learning so much. I just did a total gravel change with a 50% water change...