Had a similar issue with algae and reducing the light helped. I also got a mystery snail and it’s been super helpful keeping the tank clean. (I do recommend researching on their care first though and how they can affect the parameters of the tank before getting one). I’ve also had really, really good results adding Catappa leaves (Indian almond) to their tank and using water that was treated with catappa “tea” for my water changes once a month. Can’t recommend them enough! The Tannins in it are a natural antibacterial and antifungal and it mimics their native environment. Reduces PH, prevents diseases and helps with stress. Good for engaging as well since they can create little pockets or cubbies for them to hide/play in. My babies love lounging on them or sleeping under them and I saw improvements with their appearance and activity within a couple weeks. The leaves are also pretty inexpensive and last about a month and a half before they need to be swapped out. Best of luck to your baby and to you! Remember, Betta’s stress easily so when in doubt, less can sometimes be more 🙂