Hello everyone! I’ve got a 30gal tank that I can’t get the nitrates down in, it got Black Diamond Sand, 1 matten filter, 1 60gal sponge filter, a Aquaclear 50 with Seachem Matrix in it, I use ro/di water and Equilibrium and Flourish. There is 1-6” Bristlenose Pleco in the tank no other livestock. It’s been set up and running for about 4 months now. I’ve done almost daily water changes of 20%, I’ve over dosed Prime, I feed the Pleco every 2 days 1 waffer and a bit of flake. I just checked my water again and it’s 0 ammonia, 0 nitrite, 40ppm Nitrates, kh-1, gh-5, tds-197. I don’t have this problem in any of my other tanks and have never had this issue this long. Any help would be appreciated