I've been doing the fishless cycle in my 20 gallon for 20 days. The ammonia has spiked and it seems nitrites have finally reached zero about 2 days ago. However, ammonia was still at about 0.5 ppm yesterday and this morning. It looks like the cycle has stalled.. or something. Before, it would drop slowly (took about 3 days for 2.5 ppm to drop to 0.25 ppm), but now it's not dropping at all?! I was under the impression that the cycle is done once nitrites drop to zero. Also, the pH is quite low; about 6.2 or lower (test kit doesn't measure lower than that). Could that be affecting the bacteria that process the ammonia? I haven't tested the kH, but I know our tap water is soft. The nitrates have been dropping rapidly as well. It was > 110 ppm before. Now it is only around 10 ppm or so. I only have two live plants in the tank right now; an amazon sword and elodea. The elodea seems to be growing rapidly, but it seems odd that it would affect the nitrates that much. Any idea as to why the ammonia wouldn't be going anywhere (or if it is, very slowly)?