Your photo period is too short. With CO2 injection, 8 hours is pretty standard. Those plants are struggling and that's most likely the cause of the BBA. See how the healthy new growth is algae free? The plants are pumping all it's limited energy into new growth.
All these constant changes are are causing instability. Make a change to 1 thing, maybe 2 and stick with it. Watch only the new growth, the old growth will not recover as the plant will reprogram to the new conditions and shed old growth. This is true for slow growing plants also.
Slow growing plants should be placed in shade from the higher light plants. It can be difficult to grow both when higher light is needed. But it can be done.
Increase water changes to 50% weekly. Stop deep gravel vacuuming and try to get water turnover up to 5x to 10x water volume.
Nutrients do not cause algae, so make sure you have enough. This includes micros. Don't rely on NO3 as an indicator, know NPK and Fe. Know the ppm you are dosing. This helps alot so you can emulate what others are doing.
I would discourage the use of Glut, hydrogen peroxide is safer and can be targeted or used as a dip.
How do you measure CO2? What's the GH and KH of the tank? Using tap water? Do you test TDS?
To answer a question above; what is poor water quality? I define this by saying, it's everything in the water that I didn't put there. It is not NO3 levels. NO3 is nothing more than a nutrient. It's soluble and insoluble organics; byproducts from nitrification and waste from metabolism. The only way to remove this stuff is mechanically. 1 example would be...water changes.
I've recently read a forum post that's changed my whole thinking and I encourage you to take a minute and read it. Some top notch planted tank guys here.
My best advice, don't fight the BBA, get the plants healthy and plant more of them.
I guess links to other forums and information is a no go here. I can PM it too you at your request.