I think the problem here is plants. In a full-blown aquaponics setup, you run your FS (fishtank) at 1-2lbs of fish per gallon, and many struggle to keep their nitrate above 20-25 ppm anyway (high nitrate is good for plants.) I am running a 10g with 25 half grown guppies, planted with both emergent plants in the tank and plants stuck in the hob. 3 months of no water change & 0ppm straight across. My low tech planted 55 with duckweed gets 40% weekly WC minimum with no nitrate from the tap and I can't get such good numbers. I am not advocating 3x 10 inch fish per gallon, but I am saying that the equation is this simple: Disregarding fancy units like ATS, denitrators, carbon dosing, etc., there are only 2 things to pull nitrate out of the water: WC and plants. If you are getting nitrate out of the tap, though, WC becomes borderline useless. The only solution becomes plants, and a lot of them. You want a pound of plant growth per pound of food put into the system. Technically a little less, because of outgassing, but you also have to figure the nitrates from your tap. Some good plants are: pothos, spider, wandering jew, ivy of any kind, lucky bamboo, lettuce, they will all be happy with their roots constantly wet. Spider Plants aer great because they grow fine underwater as long as some leaves stick out. All the plants I have mentioned are, IMO, very attractive, and will grow in low light , if not well. If I remember I will post pics when i get home.