low kh co2

Hi there, based on the ph kh chart, if my 120L heavy planted tank is 0.5 Kh & 6.9 Ph, to reach 1 point Ph drop (5.9 Ph) which about is 18.9ppm. So does it mean its inadequate? Im already at 5bps and targeting at 30ppm, should be around 5.7 Ph? I have mostly soft plants like Tonina & Macrandras...