I set up a 20 gallon tank about 6 weeks ago with 1 male betta. I added TSS and didn't change the water for two weeks, at which point my results were 0,0, 5. I then left town for two weeks, during which the betta was fed sparingly and no water was changed. When I returned I tested the water and got all zeros. I did a water change/vacuum because there was poop all over the bottom of the tank. Today, once again, my test results are reading zeros across the board. What's going on?