IMO, based on my reading, preventing bga from "seeding" your tank is going to be pretty well impossible unless you set it up on the space station. BGA was one of the first forms of life on the planet and is undoubtedly one of the most successful. It produces spores that are spread by air and it grows in mud puddles, in the damp spots in your lawn, virtually anywhere with access to moisture and light. Every tank has bga (unless it's brand new), the only thing you can do to prevent it from taking over your tank is provide conditions that favor plants.
Wishing I had a pithy quote