i have had my 55 gal tank now for about 6 months. i have a few fish and few corals. 30 kg live rock. ammonia 0 nitrite 0 phosphates 0.03. calcium 420. mag 1300. kh 11. ph 8.0. sg 1.025. my problem over last 2/4 weeks is nitrates they were about 40 but now they have crept up yo 100 and i dont know why. a star fish was dying so i got out quick ut apart from that i stuffed and ideas and how can i kepp these down. i do water change every two weeks about 50 ltrs