I am not sure what "underlying problems" the OP has, though
By this I meant the lack of growth, or the lack of eye-catching growth. If he wants to "over-drive" the plants then he needs co2. adding fert's at a limited range can be good, especially NPK, but with this set-up I just can't fathom why he/she would need much more than about half EI's dosing regimen. My 33 gallon gets by just fine on food and detritus providing N and P, while I just dose sometimes with K, Fe, and trace every once in a great while. Many dependent factors though.
I had no idea 18000 k was so well pronounced in both the blue and red spectrums. I thought it would be more blue or even purple like actinic. Shows to go ya why I am a noob and over stocked is not.
With this little lighting, I think 1/2 EI is fine.
2x 20W T12 type lights, ain't much on 32 Gal tank.
This takes cares of the light/ferts, but the poster wants more growth, ferts alone ain't going to do it. They will help but the biggie is the CO2/or Excel alternatively.
If they want more growth, healthier plants etc, they should add CO2, not just ferts.
Co2 is a fert and can increase growth and health in low light tanks much more than many think.
I do not think adding CO2/Excel "over drives" a dang thing however........no more than adding ferts, or adding more light......they all 3 work together, so if anything, the poster is CO2 limited more than they might be nutrients or light limited. Nutrients are easy and so is light in this case, this leaves just CO2/Excel to monkey with and consider as far as growth rates.
There's no over driven growth here since the system is going to be light limited as far as growth, adding CO2 will just increase the light use efficiency, so they get more out of the light they have, and better growth, wider range of species and less competition among plants for nutrients/light and CO2.
You will get better growth using CO2, but it is still quite manageable.
I try not sway folks either way on CO2 or not.
Their goals with plants, not mine, dictate that choice.