I use it when I have ammonia spikes for whatever reason (unseen plant decay, whe I cycled with fish in the tank- BAD LISA!). I also have chlorine and chloramine. I don't trust that it effects other chems. but I think it helps with ammo.- I get crazy with that...don't like any in my tank...however I do water changes everytime there is an ammonia problem, so I figure it gets the ammo left behind from the water change and I need it for the chloramines. Point is it needs to go in anyway, so I like to believe it helps with ammonia.
Also if it is late or I don' t have time to change the tank, I will put prime or ammoloc to ease the ammo. until I can change the water a little later.
Lisa