120g (94g+26g) Co2 Injection Rate. Need Help In Estimation.

After alot of days tinkering with nutrients, Lights and flow rates i reached to a conclusion that my CO2 was way too bad. I just set it to 92 ml/min though ive no idea if its a overkill.

My Display tank

Diamesion 48 Inch L X 18 Inch D X 30 Inch Height.
170 Par at sustrate level
Water Degassed pH: 6.8
GH : 3
KH : 0

Sump Dimension: 36 Inch L X 15 Inch D X 15 Inch H

Filtration : X5 Turnover.
Injection Method: Cheap Diffuser.

Photoperiod 7 Hours ( 2pm-9 pm)
For CO2, I prefer half an hour window On & Off.
Weekly: Dosing 21N-15P-19K.
Substrate: ADA Amazonia Light. (I just hate it, It sucks alot of Phosphate)

My Diffuser in placed under the main Pump which makes 2 90 Degrees turn before it discharges the water into the tank. Total pipe length is around 1.5m approx.

Do i really need a CO2 Reactor for this setup ?
What flow rate in ( ml/min or cc/min ) shall i set it to target 40 ppm CO2 ?
I know its hard to measure CO2 without KH but i am avoiding it because i have plants like Tonina Fluv and Syngonanthus Belem which certainly hate Carbonate Hardness.