I would flush the stress coat and choose a different product. IMO.
There are a few reasons for getting a trace ammonia reading like you are. One would be if your water company uses chloramines. Dechlors break these down which neutralizes the chlorine part but then frees the ammonia part. Even if you use a dechlor which also detoxifies ammonia, what that does is turn ammonia, NH3, infto ammonium, NH4. The latter is way less dangerous and the bacteria can use it, albeit less efficiently.
Most hooby ammonia test kits read Total ammonia which is the sum of NH3 and NH4. So to get an accurate rrading you need to test soon after dosing, Otherwise you can get an anmmoja reading ovr the next day or 2. But .25 ppm of NH4 is safe for quite some time.
The next reason you may be seeing that .25 ppm is that it is not real and there is no ammonia. Some things in our water can interfere with an ammonia test. iron is one example. Our test kits are not exact scientific instruements. In a lab a decent ammonia test rund from ove $100 to into the $1,000s for the really exacting applications.
So, how can we get some idea of what is actually going on in your tank? And here is how I explain it. Kets suppose I were to ask you to do the following:
1. Set up an aquarium.
2. Out in .25 ppm of ammonaia.
3. As soon as that starts to drop, add nack enough ammonia to keep the tak at .26 ppm. if you test in an hour it will be .25 or in a day or a week, it will always be .25.
Now all you have to do is tell me how you can make that happen. And that will explain why it is virtually imporssible to have a contant low level reading of almost anything in a tank. Do not forget that ammonia is a gas. So as long as your water's pH is above 6.5 or so, some fraction of the ammonia will be NH3 and able to evaporate. As soon as it does, some of the NH$ will become NH3 to restore the balance.
So, as long as that .26 ppm stays constant and does not rise, it is likely not an issue. If you want to be sure, read the section in the article here on Rescuing a Fish-in Cule Gone wild. It will provide you with a link and exact instructions on how to know exactly how much of any total ammonia reading in your tank is in the form of NH3 and the rest will be NH4.