Today was vacuum day for my betta's 5-gal, which I do once a week. I use this to do a 50% water change. After cleaning up and doing the change, I waited for any extra debris to settle before testing the water. Everything was at the proper level, except nitrates and nitrites. They were a little too high for my liking. But why would they still be so high after a 50% water change? Just in case, I did an additional 25% water change, waited again for the water to settle, and took another reading. Nitrates were good, but nitrites were still up a bit. Why is this? I'm wondering if it has to do with maybe the spot I'm taking the sample from? It's near the filter output. Also, I'm using the API 5-in-1 test strips, and I've heard those can sometimes be inaccurate, so maybe it's that? Keep in mind I usually do one or two other 25% water changes during the week. What do you guys think? Test strip error? Bad testing spot? Something else?