I have a 10-gallon aquarium with one fish.. I believe he is a silver tetra. I had him for 9+ years. Doing well, and active. However, there's an aggressive black algae issue on the gravel. I've cleaned the tank, water changes, and the problem still comes back. I haven't tried aquarium chemical cleaners or water conditioners because I don't want to disturb him.
Any recommendations, please! Thank you.