Hello My 600 litres tank is 1 month old. Water parameters: CO2 = 30 ppm Ph = 6,8 NO3 = 10 ppm PO4 = 0,05 ppm Fe = 0,1 ppm KH = 100 ppm GH = 150 ppm (JBL tests) Lightning 270 w (fluorescent tubes), 12 h 30% weekly water change (2/3 is RO water) At the beginning i had some problems with green algae, nitrates was 20 ppm therefore i lower the nitrates. Now cyanobacteria appeared but i dont understand why. According to N/P ratio there should be no cyanobacteria. I thing PO4 level is too low therefore i want to add KH2PO4 but cyanobacteria likes phosphates. Plant growth is not bad but i think it could be better. Plants: Hemianthus callitrichoides Eleocharis parvulus Pogostemon helferi Hygrophyla difformis Riccia fluitans Microsorium pteropus Anubias barteri Fish: 7x SAE 4x Discus 30x Neon tetras Thanks for any advice.