Tje odds are good you are getting a false reading.
Firstly, plants will use ammonia, in fact they prefer it to nitrate in most cases. Plants grow, which means they need more nutrients over time. However. your steady reading indicates the same level day after day.
Secondly, the bacteria multiply in response to there being more ammonia or nitrite than they can use. The ammonia oxidizing bacteria (NOB), under the best conditions, can double in 7-8 hours, The nitrite ones are slower and their number is more like 12 hours (again under optimal conditions).
So what we see here is a situation that makes no sense. The easiest way I can explain it is this. Lets suppose you have a tank with 0 ammonia in it. Now lets presumes your goal is to get a constant reading of . 25 ppm of ammonia daily. I am betting you test at different times a day, so we are really looking at a .25 reading almost any time you test. So now lets look at this from a different perspective. How could you replicate these results if you wanted to? Could you make this situation happen intentionally? And the answer shows why that .25 ppm reading is more likely than not a false reading. It would take some very expensive and sophisticated equipment to make this happen.
If there is a constant low level ammonia source in the tank and you have no bacteria, the ammonia must build up higher and higher, not remain constant. If you have some number of AOB in the tank then you should see a couple of things. The first is, if you have an ammonia reading, that should then be followed by a nitrite reading. There will be nitrite present even after enough AOB have established because the nitrite oxidizing bacteria (NOB) start reproducing later and do so slower then the AOB. So the two situations we expect to see are not there.
Next, If you have AOB present and you have a real .25 ppm ammonia reading, the AOB should rapidly multiply to handle it so that is disappears. So the reading should become 0 in short order. But we do not see this either.
Finally, the are a number of things that can cause false readings on ammonia kits. This includes iron in the water or the use of ammonia detoxifiers (usually found in one's dechlor).
Q: I am using Prime® to control ammonia but my test kit says it is not doing anything, in fact it looks like it added ammonia! What is going on?
A: A Nessler based kit will not read ammonia properly if you are using Prime®... it will look "off scale", sort of a muddy brown (incidentally a Nessler kit will not work with any other products similar to Prime®). A salicylate based kit can be used, but with caution. Under the conditions of a salicylate kit the ammonia-Prime complex will be broken down eventually giving a false reading of ammonia (same as with other products like Prime®), so the key with a salicylate kit is to take the reading right away.
from
http
/www.seachem.com/support/FAQs/Prime.html
One of the major issues I see with folks, especially those new to the hobby, who are cycling tanks and testing is that they pretty much always accept the test results as accurate no matter what. But the fact is that hobby test kits are not the most accurate. Sometimes they give results that do not comport with the biology and chemistry involved. If we are not aware of these to some extent, it becomes simple to assume the test kit is right and something else is wrong.
So what i believe is at work here is not 25. ppm of ammonia but rather no ammonia and a false reading. Most of our kits which test in the nitrogen complex tend to be least accurate at very low or fairly high levels.
