Looking for help!

Hey guys, my name is Antonio.
I was hoping I could find some advise and knowledge here with you all. I've started my first high Tec tank but seem to be confused on some stuff.

Set up:
-55 gallon fish tank
- 1 Finnex Planted+ 24/7 SE Fully Automated Remote Aquarium LED Fixture AND 1 Beamswork DA 6500K 0.50W Series LED Pent Aquarium Light Freshwater Plant Discus
(I use the 24/7 feature on the Finnex, the second leds turn on along side with the CO2 which is around 10 am and turns off along side the CO2 around 4 pm)
- Pressurized CO2 using a Premium AQUATEK CO2 Regulator with Integrated COOL TOUCH Solenoid
-Cascade 1500 Canister Filter

Question 1: How do I check my CO2 leves?

I've checked online and everyone says to use a drop checker, but could be slow and unreliable. The other way was to check PH and KH then using a chart determine the current CO2 level. I've done this and my PH is around 7.4 and KH is around 4. Which according to the chart is low on CO2.

Question 2: Does that mean I have to increase CO2 input into the tank even more?

But if I increase the CO2 even more would it not harm the fish? My PH from the tap is at a super high 8.3 so having it at a 7.4 with the amount of CO2 I use now seems like a huge change already. Is it ok to increase CO2 levels even more, or em I doing something wrong, em I testing PH or KH wrong perhaps?

Question 3: Why don't my plants look lush and green?

The plants are growing fine, pretty fast actually.
But they don't look lush and green. I dose Easy Green All in One Fertilizer from Aquarium Co-Op once per week and API leaf zone once per week on a different day. Em I not dosing enough?