Yeah it still shows up mate. But you know its not toxic if you have used Prime. Its also good to note (Prime aside) the lower the PH, the less toxic ammonia is - but naturally that does not mean to rest up on water changes. Lots of big water changes is the key then gradually move back to your usual 2 - 3 times weekly (depending) is the best way. I say this only because you can treat for current ammonia using Prime but more ammonia can build up and if you have only treated once - thinking that its all clear may lead you down an awful track.