So for the last 2-3 weeks my nitrates have been at above 40 ppm for no obvious reason. I have about two thirds of the tank planted, my tank is 11 gallons (14 US gallons) and there is exactly 11 inches of fish in the tank. I feed enough that most or all fish get some food, once per day missing out two days a week, but I am careful to not over feed and remove any uneaten food. I have done like 7 or 8 25% water changes in the last two weeks, and the tap waters nitrates are around 15 - 20 ppm, but 24 hours later it would have doubled in the tank. So after no improvement after doing 25% - 35% WCs around every other day, I am thinking I might do a 75 - 80 % WC and then use nutrafin cycle to bring in new bacteria. (Also my tank is 4 months old so I am pretty sure its cycled. There is 0 ammonia, 0 nitrites but 40 - 50 nitrates) My only idea that could be causing the high nitrates is that my betta killed like 3 red cherry shrimp between 2 - 1 months ago and they could be decaying somewhere, but I doubt it.