I set up a QT last night, added salt water, a heater, a thermometer, and an air pump. I plan on adding some PVC but still have like 2 days before I get my fish. The last thing in it is a Seachem ammonia alert. It hasn't been 24 hours yet, but the ammonia alert has gone from "safe" to a little bit between "alert" and "alarm". Is this normal in an empty tank? What would be causing the ammonia?