I have 40 lbs of dry marco rock cycling in a tub with a powerhead and heater (78 degrees). I added the rock to the tub on 12/10, dosed ammonia to 2 ppm, and added 6 capfuls of microbacter start xlm. On day 2, ammonia was down to 1 ppm measured with API. On day 3, it measured .5. It then stalled on .5 for 4 days (12/12-12/16), during which time I added another 4 capfuls of Microbacter start. On the 17th my ammonia read 1 ppm again, and has been the same ever since. I added some prodibio biodigest and more microbacter start today as well. How is it possible that the ammonia is rising instead of falling? I was excited to see it falling so fast the first few days and now I'm really scratching my head. There is no source of ammonia and plenty of bacteria being added. The test tube is rinsed after every test and then rinsed with the tub water before testing. What should my next step be here?