OK, so moving on to plan B. I am finding the control of BBA extremely
time consuming. It's the most tenacious algae. Hell, I don't even get
green spot algae anymore. BBA grows very slowly, but it still bugs me as
it excludes me from keeping very slow growing plants.

I have a spare 110 litre aquarium I wish to move all my fish into from
the 330 litre, temporarily. Given that the main tank will have no fish
in it, how far can I push a treatment to guarantee a kill of BBA and
still give the plants a fighting chance? For example, how many days of
blackout would be required, 3, 7, 14 days?? I presume I'd stop all CO2
for that period.

Plan C is to strip the tank.

Nikki