I heard of lava rock that: 1. it breaks down quickly if used in an upflow context; and 2. it stains the water.

****Does it stain the water only if you dont rinse it will before initial usage, or evenso eventually?

Will bio bacteria cling to zeolite?

I like that zeolite can be recharged in a salt bath, however if the pond has salt it will release some amonia and other toxins, but that might not be important considering that its not adding in actuallity but only returning what was already there and what would be there if it was for only having lava rock.

I have a lot of lava rock in my pond filter. It has hardly broken down at all since 1997. It has not stained the water either. New lava rock may contain dust but that can be rinsed out as you said.

Good bacteria will cling to any surface including zeolite. Zeolite is rechargeable in concentrated salt baths (which would kill the good bacteria). I put in a box of Ammo-Carb (carbon and zeolite) once a year in a filter bag in my filter. The active sites are probably full after a week but I leave it in there where it acts like a general addition to the filter. You're right, any ammonium cations (NH4+) released into the pond because of exchange with sodium cations (Na+) would have already been in there in the first place. If zeolite is being used to remove high ammonia, it should be used for a few days and then removed (or recharged elsewhere). Zeolite is not a replacement for a healthy nitrogen cycle.