I can’t see it mentioned, but what about trying to manually remove? Just a tooth brush here and there. BBA will wither away once everything else grows in (in my experience). Though I don’t believe you can truly eradicate it.
Put this fish in a bucket for a few days and go in with a heavy application of easy carbo?
You might be dosing too much, feeding too much, or perhaps needing to cut your tank water with rain water.
I personally run tanks lights at around 60% for 10+ hours, but I use floaters to diffuse that. I don’t think your plants are getting enough duration of light? 5.5 hours is pretty much their normal night hours 😅 if you watch the floaters grow, you can use their growth as an indicator of when you should add frets to the water.
If you’re this way inclined, look at getting some ramshorns, they do a lot of good work of stopping algae before it starts.