My new ranchu is in a 20 gallon quarantine tank with a 200 gph AquaClear filter (which contains a sponge and a bag of zeolite). I am testing two times per day for ammonia and none has turned up so far. When it does, how do I recharge the zeolite bag with salt water? How long does it need to soak in what concentration?

Supposely, in an agitated solution of salt water, the zeolite will drop it's ammonia within 1/2 hour. I prefer to leave it longer.

Usually I make up the solution - and make sure you have enough water volume that it can hold the concentration of ammonia you will be releasing - and drop the bag of zeolite into the salt solution. There it stays, until 2 days later when I rinse it well and replace the bag that is in the filter with the recharged bag. The bag removed from the filter gets a new solution of salt water to soak in for a couple of days.

I do not wait for the tank to show ammonia. When the zeolite stops binding ammonia it STOPS. It is an on/off one/zero type reaction. There is no taper off. So if you have a fish putting off a lot of ammonia, your tank can go toxic within hours. So I usually test test test, yes, but also exchange the zeolite bags on a regular basis.

Salt sold for water softeners is MUCH cheaper than aquarium salt for recharging zeolite. I smash up the salt pellets - or simply dissolve them. For about 3 bucks, I get 50 pounds of salt.