Zeolite works as an ion exchange by absorbing and binding certain substances. In the saltwater aquarium, zeolite is used in a special zeolite filter and must be constantly flowed through. The zeolite rocks binds ammonium, which is the precursor of nitrate and nitrite. It therefore effectively reduces the nitrate and phosphate levels.
The rock also serves as a settlement area for important nitrifying bacteria. Zeolite is most effective when it is agitated approximately twice a day via a shaking function in the filter. So bacterial deposits are removed and made available to the skimming.