How do I know I need ferts?

Just set up a new tank (also new to planted tank hobby), how do I know I need ferts? Can I still get thriving plants without ferts?


-caribsea floramax substrate
-aquaclear powerhead+filter
-finnex ray2 (at my substrate level I should be getting around 65-75 PAR)
-currently planted with hydrocotle japan and dwarf hair grass (aiming to carpet, both)
-paintball CO2 running 2bps thru a glass ceramic disc diffuser(powerhead also chopping the bubbles)
-w/c 50% weekly (conditioned with Prime)
-daily dose of Flourish Excel

Trying to prepare for if I need to start a dosing regime. I don't want some outbreak to happen and then conclude the solution to be lack of ferts. (or exhibit slow/stunted growth and find out its due to ferts)

Thanks PT