The first hour or so is the most critical so getting your c02 optimised for lights on is very important. Keep tweaking it up until you get it at lime green for lights on and hopefully this will help with the issues you are beginning to suffer with the plants If you continue to have issues then you need to up c02 further, reduce lighting intensity and look at distribution.Thank you Iain I have followed your suggestion and increase the CO2 coming up by half an hour as the dropchecker is already lime-green/yellow for most of the photoperiod with the exception of the first hour or so.
Cheerio,
Ady.