Why is ammonia not budging???

I have had this annoying "ammonia spike" of 0.25ppm for a week now maybe a little over a week and I have treated with zeolite crystals (which claim to remove ammonia), Prime to detox the ammonia, Stability to boost my bio filter and done 12 gals of water changes. (i have a 20gal long). The **** tank still reads at 0.25!!!! Everything in my tank is thriving though. My 2 clowns, Trumpet coral, Duncan, Zoas, and Hermits.



I feel there is no way that my tank really does have this consistent spike for this long with all of these treatments. To my knowledge I should have seen some sign of improvement by now. What do y'all think? I think my ammonia test is malfunctioning.