Zeolite types of media do an amazing job getting rid of ammonia. Given that track record, why not use zeolite in your filter all the time? That's a good question, and one that has been pondered and discussed by many. Although opinions vary, most agree that zeolite is great for emergency situations, but is generally not ideal for on-going long term use. To understand why, let's start with by explaining what zeolite is, and how it works.

What Is Zeolite?
Zeolites are highly absorbent porous minerals, composed largely of silica and aluminium. They are useful for their ability to capture and hold a variety of undesirable materials, much like a sponge absorbs water. However, not all zeolite is created equal. How the zeoilite was formed impacts it's makeup, and consequently which applications it is best suited for. Clinoptilolite, or Clino, is a naturally occurring form of zeolite that has a particularly high affinity for ammonia, making it a desirable media material. In addition to the various natural forms of zeolite, there are now artificially created forms of zeolite which differ from natural forms in their makeup.

When choosing zeolite for your aquarium, select one that is labeled for specifically for aquarium use. For instance, most cat litter contains zeolite, however it's not formulated for aquarium use, and I would not recommend using it. There is zeolite formulated specifically for freshwater aquariums, as well as for both freshwater and saltwater aquariums.

Either formula is suitable for freshwater aquaria. There are also some formulas available that combine activated carbon and zeolite, a combination that is well suited to a newly set up aquarium that is experiencing a severe ammonia spike.

What Zeolite Does & Doesn't Do
Zeolite formulated for freshwater aquarium use will readily absorb ammonia, making it a useful media when dealing with ammonia spikes or potential spikes. It is important to know that zeolite does not remove every undesirable toxin in your tank, nor does it work forever. In fact, it becomes saturated fairly quickly, at which point it no longer provides any benefit. Generally within a month or less it is exhausted and should be replaced or recharged. In cases of extremely high ammonia levels, the zeolite may become exhausted in two weeks or less. When ammonia levels are elevated, always test frequently, replacing the zeolite as needed to until the desired results are achieved. Once the ammonia has been eliminated, remove the zeolite.

When Not To Use Zeolite
Experts disagree on the value of using zeolite in a newly set up aquarium. Many, including myself, feel the biologicals should be allowed to develop naturally. However, if an dangerously high ammonia spike should occur, the use of zeolite on a short term basis is warranted. This is true even in a newly set up aquarium, as ammonia poisoning can quickly prove fatal in those situations. However it is advisable to remove the zeolite once the ammonia levels drop. Zeolite should not be used on a ongoing permanent basis. Instead it should be removed and replaced with standard media, such as activated carbon.

Zeolite formulated for freshwater should never be used in saltwater or brackish tanks. The effect on the water chemistry can be lethal for corals in saltwater aquariums. Nor should salt be added to a freshwater aquarium when zeolite media is already being used. Adding salt can cause the zeolite to release the ammonia it has absorbed, causing a sudden and potentially dangerous ammonia spike.

Placement in Filter
Zeolite is generally provided in a form similar to carbon media, and is placed in a bag within the filter. It may be purchased in lose bulk form, or already measured into media bags. In a canister filter the zeolite should be placed inbetween the foam or mechanical media, and the rings or biological media. Some manufacturers offer a zeolite pad that can be cut to fit in a power filter or fitted next to the foam in a canister filter. Zeolite may also be placed in a bag and hung inside the tank directly in the water flow, instead of being placed inside the filter. The advantage is ease of removal and replacement, which is particularly useful if frequent replacement or recharges are anticipated.

Recharge or Replace Zeolite?
Zeolite used in freshwater aquariums can be recharged by soaking it to a 5% salt solution, which causes it to release the ammonia it has absorbed. After soaking for 24 hours, spread it on a cookie tray and allow it to dry in the sun for a day or two. A faster alternative is to bake it in an oven for a half hour to an hour at 350 degrees to dry it out. The advantage of sun drying is that the zeolite may be left in it's orginal bag, which often is not safe to subject to high temperatures. Obviously given the amount of time the recharging process takes, many do not feel the effort is worth it for small quantities of zeolite.

As previously stated, zeolite must be removed once it is exhausted. If the ammonia is gone or nearly gone, it is not necessary to replace the zeolite in the filter. Instead use standard media. If zeolite is recharged, it should be discarded after two to three months of use, and replaced with new zeolite.