I have api freshwater testing drop kits and I have the tetra brand testing strips. The api kit read 10 nitrates but the strips read 200+ nitrates. I feel like that's what is slowly killing my cories. I did a 60% water change and the water strip tests still came out 200+ nitrates. I tested my tap water and the nitrates come up at 0 to 5. So I tested certain portions of my tank water with tap water and in order to get nitrates down back to normal according to the testing strips I'd need to do a 90%-95% water change. How would you guys recommend I do this? As long as the fish are in there the nitrates will continue to build up. What do I do and why are they so high?????? There's no ammonia and no nitrites so that's good at least. All other levels are normal as well. I have 4 hifin black skirt tetras, 1 teen bristlenose pleco, 7 assorted cories, and 1 adult female red crown bovilian ram in the tank right now. All seem to be doing well enough but I can tell the ram is really irritated at times.