Aqua Clear Ammonia Remover, 20-Gallon (Pack of 3)

Q: How often should the aquaclear 20 ammonia remover be replaced in the filter?

I think it depends on the type and quantity of the population of your tank and acidity of your water. Mine is high acidity and toward the cool end of the allowable temperature spectrum. I have a 10 gallon and at the moment only 3 fish. Hard winter. My filter has 3 elements - sponge, charcoal and ammonia striate. Each month I do a water exchange and replace one of the 3 elements in rotation. When I had more fish, I expedited that schedule to a 2 or 3 week cycle. Now that spring is here, I am going to deep clean the tank and rebuild the population and go back to the 3 week cycle. There also is a product from Aquaclear that combines the functions of charcoal and ammonia remover into a single pelletized product. I think their recommendation is a monthly change but I'm not sure. Do not change all the elements at once. Rotate in some fashion.

Q: For a new tank, how long would you have the ammonia filter in it? I haven't added fish yet. Also, does this replace one of the three filters?

I always keep the ammonia filter in my tank. For a new tank I'd leave the filter running in treated water for 24-48 hrs. Always worked for me. Yes it is part of the 3 inserts. On bottom is sponge, then charcoal, last and on top ammonia reducer. I change all 3 about every 4-6 weeks. I have too many fish though, so I change regularly.

Q: Can I replace my topfin filter with these rocks?

No, these rocks are specific for ammonia removal and the water needs to keep flowing over them to be effective. The filter cleans out a lot of bio trash. Short of using an ammonia test on the water, there is not real way to determine how often to change the rocks. The rate is governed by the number of fish and the size of the tank.

Q: 1. is this zeolite 2. how often are you supposed to change this

I don't know if its Zeolite. I clean my filters two times a month then replace them. I do not replace the form filter at the same time as my others. I take out 1/3 of the water once a month then replace it with fresh water that will also keep you fishes healthy and happy.