Hello Everyone... I recently lost my 7 year old Comet Brutis to high Nitrate poisoning.. He was 17" long and a great fish. My situation/timeline 2008-2014 I kept a 75gallon tank with 2 or 3 large comets. No problems. I used a magnum 350 filter with Bio wheel and a Fluval FX5 with porous lava rock in the basket. I always fed the fish 3-5 times daily they were pigs. I changed about 50% water monthly and the media in the filters about every month and a half. Never any partial water changes. Never lost any fish. Lived in the country with a well (different location than below) Spring 2014 I upgrade to a 210 gallon dual overflow tank. Using 2 fluval FX5 filters. I threw out (dumb move I know) my old porous lava rocks and started with all new Seachem Matrix rocks. I then started using the Seachem Purigen 100ml pouches (2) one in each filter. I use gravel about the size of a pea (river rock) and I believe I had it too deep as I developed little white worms (Planaria). I began to remove rocks. I use all plastic plants, an old steel beer can, golf ball, and a driftwood stump I found and cleaned up. About the 3rd month Brutis starts sitting around a lot, not moving or eating. His normally clear fins are showing red. By the time I figure out that he is being poisoned I tried like hell for about a week with daily 25% water changes, introducing aeration, and stopped feeding to no avail. He dies, but I have 2 other comets 15â€-16â€ long that were not affected (visually) I get my water tested at the Pet Shop. My nitrates are as high as can be measured on their color sheet, around 160. A few weeks later I get my own water testing kit. Today I test my water and it is super high again. I live in the country and have well. Itâ€™s a farming community and after testing tap water I cannot tell the difference, as they both have high nitrates. What can I do to lower these nitrates on such a large tank? Please helpâ€¦â€¦..