Most ammonia remover is a naturally occurring mineral called "zeolite." It's often marketed as "Ammo Chips" or "Zeo Prep". Even the filter pads are standard floss impregnated with zeolite powders & resins. This mineral works by absorbing ammonia, and when you soak it in salt water, it releases that ammonia back into the water. They're not 100% effective, and each time only release MOST of the ammonia, depending on other things in your water (iron, specifically- that stuff binds iron like MAD, and iron doesn't come out of it ever), so that every time you recharge it, it becomes less and less effective. Filter pads are supposed to be way less effective at recharging, and for some reason, they don't recommend you recharge them. I don't know why, if they're actually less effective or if the companies making them just want their money.
Anyway, for years, everyone said don't ever use zeolite in saltwater. Now it's been established that it WORKS in saltwater, albeit at a reduced rate. The salt in the water prevents the zeolite from absorbing the full amount of ammonia it could otherwise. I've heard you should use 2x the zeo in saltwater setups. But when you change the salinity at all- poof, all that ammonia absorbed dumps back into the water. So you have to be EXTREMELY careful when using it in salt, and it is NOT recommended.
