BTW: there are two types of ammonia measurements.  Ammonia exists in two forms, "Free ammonia" (NH3) and ionic ammonia (NH4+).  Free ammonia is a dissolved gas, while ionic ammonia is part of a chemical molecule with other ions.  Free ammonia is extremely toxic compared to ionic ammonia.  Ionic ammonia is not toxic, but it won't stay in entirely in ionic form.. read on.

There is a relationship between pH, temperature and and the free vs ionic ammonia levels.  The higher the pH, the ionic form tends to shift into 'free' form.  Thus a simple pH shift can convert a tolerable ionic ammonia level into a lethal one in the blink of an eye.

Most tests that you get in stores measure ionic ammonia.  Seachem's tests will tell you both, and the 'ammonia alert' is a gas diffusion test that measures 'free ammonia' directly since that is the one you're really scared of.

To be clear, you can have two tanks that test the same levels on the 'total ammonia' scales, and yet one can be tolerable to fish, while the other can be absolutely lethal.

I've found this out the hard way.  Our tap water pH is 9.2, and that tends to cause relatively low levels of ionic ammonia to change state to free ammonia.  Doing a large partial water change has killed my fish!!!  (I did a 50% change, and when I came back 30 minutes later the ammonia alert was dark purple and the fish were dead).  My test tube kit showed nothing particularly bad.

According to this: http://ce.ecn.purdue.edu/~piwc/w3-research/free-ammonia/nh3.html a pH increase of 1 point will cause the free ammonia equilibriuum ratio to increase 10-fold.  (hardly suprising given that the 1 point is a 10-fold increase in alkalinity as well).

Anyway, this experience and other factors finally forced me into building an auto water changer so that I can now automatically do two 5% water changes every day, without fail.  My problematic murkey tanks all cleared up, my unexplained fish deaths have reduced, and unfortunately my population explosion has become much worse.

Incidently, this equilibrium ratio is what ammonia detox chemicals try to mess up.  They introduce another ion to the solution that binds so darn tightly to the ionic ammonia ions that very little 'free ammonia' forms.

Also, this is why the two-chemical test-tube ammonia tests use two chemicals.  One is the indicator, the second is a strong alkaline chemical.  The second one causes the pH of the test tube solution to increase well beyond pH 12 in order to force all the ionic ammonia to convert to 'free' ammonia for measuring.  But here's the trick, the indicator agents in the new tests (yellow through green) bind less strongly to ammonia ions than the 'tetox' chemicals do.  As a result, they dont 'see' the "detoxified" ammonia.  So what "Amquel Plus" and "Ammo lock" are doing is introducing a chemical that holds onto ammonia so tightly that it has very little chance of converting into free ammonia, and so tight that even the new-style ammonia tests won't see it.  And since it can't convert to free ammonia, it can't poison your fish.

This is why you should avoid ammonia detox chemicals during tank cycling.  The extremely tight binding makes it very difficult for the bacteria to break it down.  If it doesn't cause it to starve and die, it will certainly slow its growth   You really don't want it in there.  In my opinion, steer clear of 'ammo lock' (and to a lesser degree, 'amquel plus') type chemicals during cycling.