Do not rely on your test kit to read accurately after dosing the ammonium Chloride, Trust that is will provide the concentration of ammonia advertised. If there is any bacteria that can use ammonia (and this can be more than just the nitrifiers) it will start dropping as soon as the ammonium hits the water. Testing is fine but not to indicate the level of ammonia right after dosing. If you are also using One and Only, then it changes the results from what am unseeded cycle is expected to generate.
Next, some years ago Dr. Hovanec changed the formulation from 1 drop/gallon to 4 drops. Read the bottle label for the ammonium chloride. For larger volumes it would be a PITA to have yo do drops. In a 100 gal. tank that would be 400 drops. Instead you can use the following information from Dr. Tim:
1 ml = 20 drops
5 ml = 1 teaspoon = 100 drops
15 ml = 1 tablespoon = 300 drops
We do not fill our tanks to 100% of the water capacity, We leave some space at the top and we usually are adding decor and substrate, All of this decreases the total volume. Dr. H suggest using 80% of the advertised volume. I usually use 85%. Either one is fine. The amount we muight over or underdose will not make a significant difference. Also, one's substrate will host a fair amount of the needed bacteria. If you go bare bottom, it will take longer to complete the cycle as the bacteria have to multiply in the fewer better places for them to be.
It is important to understand that the test kits we might use come in two varieties based on the measurement scale used. Dr. Hovanec is a scientist and they use the Nitrogen scale. This means it measures only the nitrogen aka N. So 1 ppm of ammonia (NH3) = 1 ppm of nitrite (NO2) = 1 ppm of nitrate (NO3). However, most hobby test kits read using the Total Ion scales. This measures all of the components, the Hs and the Os.
But as we can convert between miles and kilometers or pounds and kilos etc, we can convert the two test scales. The conversion for Total Ammonia-N (NH3 =NH4) is ammonia-N x 1.28)
Nitrite- N (NO2) is nitrite-N x 3.28
Nitrate -N (NO3) is =nitrate-N x 4.23
What the above means is that if you are using a Total Ion test kit like the very popular API ones, when Dr. Hovanec says to dose 4 drops/gallon (or 3.75 litres) to produce 2 ppm, he is using the Nitrogen scale. The API kit will measure this concentration of ammonia as 2 x 1.28 = 2.56 ppm . And the 5 ppm of ammonia-N scale that we should exceed is 6.4 ppm on thh API kit. For 5 ppm of nitrite-N the API kit would measure it at 16.4 ppm. But that kit only goes to 5 ppm. Finally, nitrite-N numbers get very high. 20 ppm of Nitrite-N = 84.6 ppm on the Total Ion Scale.
So, if one is targeting 3 ppm of ammonia using thei API test kit, they need to add more which would require a slightly higher dose. Here is the math 2 drops = 2 ppm-N = 2.56 on the APi kit. Rounding down to 2.5 the dose is 2.5/3.0 = 83% of the targeted 3.0. This means the dose is .17 short. 4 x 1.17 = 4.68 drops per gallon.
This can be a bit daunting for calculating in smaller tanks since we can not measure partial drops. But we can also redo the math. So in 10 gallons of water the dose to get to 3 ppm would not be 40 drops but rather 46.8 and I would round up to 47.
However, for most tanks just using the 4 drops/gallon and producing just 2.56 ppm of ammonia will be fine. The exceptions would be if one has water which is 8.0 pH and above. The reason is that, in a higher pH, ammonia is more toxic. So while a tank at 7.0 and 80F can have .5 ppm to Total Ammonia, but the amount of NH3 in that total would be 0.0033 ppm. This is not a problem especially in shorter time periods. But raise the pH to 8.5 and that becomes 0.086 ppm which is not safe. My rule of thumb is when NH3 hits over 0.05ppm, action may be needed in tanks with a higher pH and temperature. These calculations were done using an ammonia calculator you can find here
https://www.hamzasreef.com/Contents/Calculators/FreeAmmonia.php
Do not keep adding ammonia willy nilly. It does not require a lot of ammonia additions to complete a fishless cycle. When I am dosing ammonia into either an individual tank or my bio-farm, I measure the ammonia using the dosing measurements I listed above. I do not test after I add the ammonia. I am testing at 12 or 24 hour intervals dependin on the situation. When the end of the cycle is close, I tend to test in 12, JIK. If the tank clears the ammonia in 12 and there is also 0 nitrite, the tank is cycled. But if the ammonia is not 0, I do not test the nitrite and I wait another 12 hours and test again. The finish line is when we can add 3 ppm of ammonia on a Total Ion test kit and have 0/0 readings for ammonia and nitrite.
Lastly, if one uses seeding of bacteria, either from a viable bottle of the right ones or if one uses filter squeezings and.or decor from a well cycled tank, this wull change the numbers one will get when they test. Ammonia should not get as high and Nitrite may noy even show up. The reason is when we seed a tank we are adding both types of bacteria. This meabs whatever amount of ammonia can betirned into nitrite, there should be enough of thos ebacteria to process as soon as it appears. So if you do seed a tank, be aware that you are not waing for 1 then the other bacteria to apppear, they are both there. All we are waitning for is to be able to add about 3 ppm of ammonia and have it be 0 w/i 24 hours and for the nitrite to be 0 as well. That is the holy grail of the cycling process.