Updating again, you'd think I'm trying to be consistent.
CO2 has been running 24/7 at about 1 bubble per second and just showing green on the drop checker and I am impressed.
My dwarf sagitteria has shown visible growth and my pogostemon helferi has taken off!! A couple of sprigs have literally tripled in size. The swords and vals all look healthier and the HM turned into a huge bush which I've now chopped back to about 3" tall.
My java fern is even growing happily and looks great.
I'm kicking myself for having taken so long to get the CO2 running but now, even with my comparatively low light I can tell I'm going to have to do a lot of trimming and gardening, hooray!
The fish all seem happier with the removal of the furcata rainbows but I found an oto which had jumped. There is a 1"x1/4" gap at the back of the tank where the lid isn't quite snug and he somehow made it out of there to become fish jerky.
The new shamu log is in and still trying to float but I've got it wedged under the pump outflow tubes so hopefully it finishes waterlogging and sinks. Fingers crossed, I really don't want to have to screw it to a tile and tear the entire tank up just to get it placed.