Chloramine is created by combining chlorine and ammonia. When dechlor is used it breaks the bond. The chlorine is detoxified and that leaves a small amount of ammonia. Consider that when we do a fishless cycle we are adding 2 -3 ppm of ammonia. There are bacteria to handle that sort of load.
The residual amount of ammonia created when the chloramine is broken down is minimal. To start, nost of the ammonia in water is actually in the form of ammonium. So it is already naturally reducing the ammonia level that way. Then the bacteria are at work and they quickly use the small amount of ammonia that might be present. And the bacteria can process ammonium as well, They just cannot do it as efficiently as they can use ammonia.
And the ammonia test cannot see the ammonia in chloramine because it is not there as ammonia until the chloramine breaks apart. That happens when the dechlor acts on the chloramine.
The other thing to know about all of this is how to tell the difference between a real and a false reading in the range of .25 ppm of ammonia. The biggest clue is if the reading is real then the bacteria will multiply to handle that excess ammonia. but if the reading is always there whenever you test, it is almost certainly a false reading. It might be the result of a bit of iron in the water.
It would require many $1,000s in sophisticated equipment to create a persistent reading of ,25 ppm of ammonia that never changes. That is, it never rises and never goes down. Ask yourself if you wanted to create that result, how would you even achieve it? Bear in mind that what triggers the bacteria to reproduce is more ammonia (and/or nitrite) than they need to thrive. Raise the ammonia level and the bacteria reproduce to handle the higher level and the ammonia reading goes to 0. Reduce the ammonia level and the bacterial colony shrinks to stay in balance with it's food supply.
On the other hand if they did not reproduce than the ammonia would accumulate and the reading would have to go hiogher than .25 ppm. One of my greatest beefs with the internet and fish keeping is when I read somebody stating that if you have a reading of .25 ppm of ammonia you ust di a big water change ASAP. In almost no situation is that the case.
What determine how much of any total ammonia reading is ammonia and what portion is ammonium depends upon the pH and temp. of one's water. Temp is a much less important factor than pH. So lets assume one has a tank at 78F and an ammonia reading of .25 ppm. What pH must the water be to cause the to be enough ammonia to be a problem?
The answer is the pH must be higher than 8.6 to result in tha ammonia level being at 0.05 ppm. Many fish can handle that amonunt of ammount but more sensitive fish and other critters might not be so safe. I use that .05 ppm of ammonia as being the red line even though a bit more might be OK, better safe than sorry.
Incidentally, the above facts are why I do not acclimate fish I get shipped in. During the trip the fish are doing two things, The first is breathing and that creates ammonia. it also creates CO2 and this creates some carbonic acid which cause the pH to drop. That drop in the pH keeps the ammonia in the ammonium form. When I open the bag it lets out the co2 and lets in oxygen. This causes the pH to rise which turns some level of the not toxic ammonium to turn into ammonia. So, just this fact is enough reason for me to want the fish out of the bag water ASAP.
When I ship fish I put a small piece of PolyFilter in the bags. It can absorb all sorts of pollutants including ammonia and organics. So it helps keep the water safer during the trip.
https://www.poly-bio-marine.com/
