That makes sense bc I have read that low ph means ammonia isn’t toxicA little provoking, perhaps, but it is an honest hypothesis. I hope the hypothesis can offer some insights for everyone that enjoys the hobby and cares about their fish. It feels a bit like arguing the world is actually flat, not round. Or the other way.
The N Cycle
Biology has a lot of cycles. Nitrogen (N) cycle is one of them. Cycling is a continuous process where ammonia is excreted by animals, as a byproduct of protein metabolism, and also released from decaying organic matter. The ammonia is assimilated by plants, algae, fungi and micro-organisms. These organisms are consumed by other (heterotrophic) organisms. This is how N enters fish again. This is the N cycle in a nutshell.
Cycling a tank
The assumption by many hobbyists
When it comes to cycling a tank, all eyes are on the micro-organisms. The so-called beneficial bacteria.
An ammonia source enters the water column. "Beneficial bacteria A" convert the ammonia to nitrites. "Beneficial bacteria B" convert the nitrites to nitrates.
This happens mostly in the mediafilter.
Once you measure only nitrates, the cycle is done. By cleaning your filter and conducting water changes, you take out the nitrates.
The assumption by science and some hobbyists
The beneficial bacteria consume oxygen and don't require a lot of physical space. They reside in biofilms as the bottom layer. In biofilms, oxygen is pretty much depleted by these and other bacteria. Hence, these biofilms prefer oxygen rich areas. The benefits of an over-sized canister filter with the best filter media in the world, is silly and driven by suppliers and retailers. You need good flow of oxygen-rich water. Inside a filter or outside the filter (so inside the tank) -it doesn't matter.
(Or you need plants. They take care of ammonia AND they offer oxygen. In planted tanks, any filter plays the second violin.)
These beneficial bacteria appear to be many different species. Depending on water parameters (KH, temperature, oxygen), certain species dominate over other species. And species that appear initially in a tank, are very likely not the same species that we see a few months later. The bacteria that convert ammonia to nitrites might be taken over completely by bacteria that convert ammonia directly to nitrates. And, technically, some or perhaps all of these bacteria might not even be bacteria, but archaea.
Hence, it is fairly useless to direct the cycling process. Just sit and wait. Like you would when releasing and testing ammonia the whole time.
When people test the water for ammonia, they assume that ammonia in the water is dangerous to fish. This is not true. Ammonia is dangerous inside fish. Ammonia is a byproduct of protein metabolism, that fish want to get rid off. Almost all freshwater fish excrete ammonia mostly through the gills. As long as fish are able to excrete ammonia, they are fine. When fish no longer are able to, it becomes dangerous. Ammonia builds up and causes damage.
One way it causes damage is ammonia, as NH4, interfering with potassium channels.
NH4....? Isn't this supposed to be the non-toxic part of ammonia?
Inside fish, ammonia is mostly present as NH4 because of the internal pH (7-8). NH4 becomes toxic when it starts to build up.
Due to the workings of the gills, ammonia passes the gill membranes as NH3 - the "toxic part". NH4 doesn't pass the membranes in freshwater fish.
Because the pH of the water is most often below 8, the NH3 converts to NH4 in the water.
NH4 is considered non-toxic because it doesn't pass the gill membranes. NH3 is considered toxic, because it passes the gill membranes.
When ammonia becomes dangerous
What happens if the pH of the water surpasses the pH of the fish's blood? This is the crux.
Fish are no longer able to excrete ammonia as NH3, and ammonia, as NH4, starts to build-up inside the fish.
So while you are occupied measuring the ammonia in water, fish don't really care about it. As long as they are able to excrete ammonia through the gills.
Fish in high pH environments
If you add most freshwater fish species in a pH 9+ environment, they will die. Some freshwater species hail from high pH environments and have evolved various mechanisms to deal with ammonia. One of the mechanisms is the conversion of ammonia into urea.
This thread was more intended as a discussion thread. I'm very much interested in reading about cases where ammonia poisoning is actually seen.
Statements like, "ammonia shows up on my test strip and now all fish are dead", are plain silly. NH4 inside the fish's blood was X and now the fish are dead, makes sense. But we cannot measure this easily of course. That doesn't make a water test strip a quick and dirty substitute.
I agree that if you measure ammonia after 3 months, your tank has serious issues and is not a healthy environment for fish. But this is part of the oxygen cycle (O) discussion. In which case, measuring ammonia is a quick and dirty substitute for oxygen.
OK, enough for now.