So two weeks ago on a Tuesday I took dead fish and a water sample to the LFS to get a refund. I got the refund but they told me my nitrate was above 160 ppm. Puzzling, because I have 3 swordtails and two GBRs doing just fine (in fact they were spawning at the time). So the following Wednesday and Sunday, and the Wednesday and Sunday of this week, I did 50% water changes (as opposed to my usual 25% once a week on Sunday) and I have yet to see my nitrates drop below 160 even though all other parameters are completely stable at 0. What could be causing this and what can I do more than 50% twice a week to see results? Also, to save time answering further questions in this thread here are the answers to some things i can see being asked: -Yes, the only stock so far is the GBR pair and the 3 swordtails and they are showing no signs of illness -This is a 60 gallon aquarium -I am using an API master test kit, got one when I found out i had such high nitrate -The tank is cycled and has been for 3 years now Thanks in advance for any help!!