I need help with my nitrates. I had my 20 gal set up for 3 months and decided to go up to a 55 gal with a refug. Every thing is good but my nitrates, I can't seem to get them under 20. I have a yellow tang , a damsel and a golby. I feed every other day and do a 10 gal water change once ever other week . I have a 4 in. sand bed and about 60 lbs live rock with a cleanup crew. My refug consist of 3 sections 1 overflow that has live rock, 2. 2 in. live sand with culerpa and cheato, through balffles and into return area. I don't know what else to do. Any advice. Perm- ph- 8.2, nitrite-0, amon.-0, nitrate 20, saltine- 1.025. Have had the 55 set up for 2 months. Thanks so much