My tank is 4 foot, 200 litres
Chihiros WRGB II Slim LED Light with Bluetooth App Control 120cm
All the settings were on 35% for 9 hours a day, with the ramp mode on
My tank is over 8 months old
Height is 50cm high, you light intensity is not high, there could be a problem with other factors:
Inconsistent CO₂ levels
Low or unstable nutrients
Low water flow areas