I don't want a non CO2 set up because i have metal halide lights and i love the look of them. I have no issues with pruning and fertilizing the tank.
Yes you would run into problems if weekly water changes were not done with EI but i am not using EI doses.
I agree CO2 levels even with my drop checker are not that accurate so my CO2 levels are between 10-20ppm. I aim for 1bps/100litres of water so i have 5bps and pH drops from 7.1-6.3. I do not know what this equates to with CO2 levels but everything seems to be growing very well at the moment.

LAKA