Hi Boon Yong,
If I read correctly, your tank is ~400L with only 108W, > 1 WPG.
This is really a low light tank. For low light tank, you usually don't have to worry abount CO2 level. Many low light tank don't even inject CO2.
Tom Barr's opinion that high CO2 level helps to elimiate BBA usually refers to high-tech tank. It should not be necessary to maintain high level of CO2 in a low light tank.
I am not sure whether it could be due to your dosing as you seems to be dosing quite a lot of NO3 for a low light tank with mostly crypts,anubia and moss. You did not mention the fish population and feeding pattern. Low tech tank may not even require dosing of nutrients if the fishes are well fed.