I was confused as you said you had done a water change 3 days ago so I wuold not expect ammonia readings to be so high that they could "go down quite a lot" as you said.
The ammonia binding products stuff up the test readings, I believe, by giving higher readings than they should. I am not sure as I do not use these products but I am pretty sure they make the readings higher than they actually are, rather than lower.
Why do you have a mix of coldwater and tropical fish in the tank?
Never believe the stores as they are usually trying to sell you something
A well balanced and mature tank should not need added products like Prime.
To get accurate readings you wuold need to stop using the Prime.