I had one tank that woukld get this species even so often, typically when I added more light, but none of the other tanks ever got any.
Nutrients. sediments etc are exactly the same and same routine.
Light is the same PAR, color temps are bit different.
So light intensity and the nutrients/sediment cannot be it, I am certain and have transferred plants from this infested tank to other tanks without issues.
The only difference unaccounted for that seems likely is CO2.
We have this Spriogyra at the lab in the vaults where I work, so spores are easily brought home.
They do not grow except in one tank. When I reduce the light= no algae, when I adjusted the CO2= no algae.
This does not imply that it's 100% direct to CO2, nor that there might not be indirect effects, but it does seem like a big factor given the observations on multiple test tanks.
Regards,
Tom Barr