Your photo period was probably what was driving the BGA. I'd probably push it back further to 6 hours/day till the BGA is under control.
I'd just keep manually cleaning it, and make sure your tank is as clean as possible (prune heavily, scrape all the walls and equipment, vacuum as much out as possible afterwards, clean your filter).
5ppm nitrates isn't bad, means your nitrates aren't bottomed out and you aren't starving the rest of your plants.
If reducing the photoperiod and manual cleaning doesn't keep it from spreading, then you might try nuking it with an antibiotic. GBA is actually a symbiotic bacteria and algae, and killing the bacteria will kill the entire organism.
I'd just keep manually cleaning it, and make sure your tank is as clean as possible (prune heavily, scrape all the walls and equipment, vacuum as much out as possible afterwards, clean your filter).
5ppm nitrates isn't bad, means your nitrates aren't bottomed out and you aren't starving the rest of your plants.
If reducing the photoperiod and manual cleaning doesn't keep it from spreading, then you might try nuking it with an antibiotic. GBA is actually a symbiotic bacteria and algae, and killing the bacteria will kill the entire organism.