I agree on the excess ammonia and the bacteria trying to catch up. It's an interesting topic. Now days I don't bother learning the species names as I suspect I have a bacterial population of many types that works in my tank. Which is why I think there is a difference between a just, cycled tank and "stable" tank running for several months after.
On the US forums it's not uncommon to have a ph crash on a cycling tank and crushed coral or baking soda to add carbonates will be suggested . Also a water change to add back anything else. This seems to help a stalled cycle. So below ph 6.5 the bacteria slow down and get really slow below ph 6.0.
However, people have cycled tanks with low ph so I've always wondered if maybe one type of bacteria prefers ph > 7 while another below. Basically if there is a gap, some sort of bacteria will fill it and a stalled cycle is really the bacteria trying to change over.
There are likely hundreds of species of nitrifying bacteria in a tank that has been "established" for over a year.
1 ppm ammonia --> 2.7 ppm nitrite --> 3.6 ppm nitrate.
For every gram of ammonia oxidised into nitrate 4.8 grams of oxygen is used, 7.14 grams of calcium carbonate is used (thus why pH crash can occur in tanks with to little buffering capacity).
My own experience is that I have crashed the filters before and had a mini-cycle. Ammonia & nitrites off the scale, huge nitrate readings - eventually sorted.
The bacteria I think are fairly tough once going properly as well. Would have the paper somewhere but the bacteria in a lab test were re-started with ammonia after several months. This matched a tank with a relative that started up fine after being dormant for months.
In Perth water I also wash every part of the filter under the hose. I've tested this by putting tap water in the canister filter over-night and then re-starting. Ammonia checks were all fine. I'd never suggest this on a forum as I've worked up this point over time specifically for my tap water & also have two other filters running but this to me says the bacteria are fairly hardy (although would be interesting to try that with Kalgoorlie tap water). Some thoughts anyways.
Edited by Delapool, 18 June 2017 - 09:53 PM.