Hey guys, hope you can help me out here. Firstly, a picture of my tank and its specs. 90cm x 45cm x 45cm ~140 litres Filtered with an Eheim 2215 and a Tetratec EX90 Lit with 4x 36W Philips 865 6500K fluorescent lights with reflectors 8 hours per day Injected with pressurised CO2 via 2 inline reactors at 2-3 bps Base is ADA Amazonia II with Shirui decorative sand Fertilised with EI: 6g KNO3 0.7g K2SO4 5.1g KH2PO4 15.5g MgSO4 Those are the weekly doses, I dilute 3x the amount in 250mL of water and dose 10mL per day which results in 20ppm NO3, 30ppm K, 9ppm PO4 and 10ppm Mg per week Traces and iron through 4mL of Seachem Flourish per day which is roughly 0.5ppm Fe per week 50% water changes once a week I have raised the PO4 dosing from 3ppm weekly to 6ppm weekly to 9ppm weekly now but the GSA just shrugs it off. It's even occurring in areas with pretty good flow like on the larger rocks in front and on the white decorative sand. You can just about see it in the photo above, but its gotten worse since I took that photo a few weeks ago. I use a permanent JBL CO2 checker just as a gauge of CO2 levels and its yellow in all parts of the tank where the GSA live. I blacked out the tank before previously and it does remove most of the GSA but it just bounces back again. I wanna tackle the rootcause rather than the symptoms. Do you guys see anything wrong with what I'm doing?