I have a 28G aquarium and started the fishless cycle 7 days ago. Added Bio day before I started adding ammonia. 1.5ml Day 1,2 & 3. 1ml 4,5 & 6. Ammonia increased from 0.25 to 4ppm. On day 4 I added bio once again. Now it's day 7 and haven't gotten a reading on my nitrites yet. What's going on? I should be getting something right?