Why Zeo-lite is Not Recomended:
Zeo-lite is a chemical that is widely available in fish stores for its ability to suck up ammonia like a sponge. There are other brand names, but any ammonia-absorbing chemical would fall under this category. One would think, "why is this so bad?" Well, this is why it can be.
1) Once zeo-lite sucks up a certain amount of ammonia, it will not suck up anymore. There is no way you can tell how "full" the zeolite is until you suddenly have ammonia levels in the water and this could make your fish sick or weak. Granted, zeo-lite can be re-charged by soaking it in a container of salt water, its powers are not easilly monitered.
2) You can NEVER add salt to an aquarium with zeo-lite. Salt is useful in many ways, treating many types of diseases, helping wounds heal, and of course its mandatory in aquariums with brackish fish. Like said above, any salt in the water will cause the zeo-lite to let go of all the ammonia, immediately causing highly toxic and dangerous levels in your aquarium.
3) The most important downfall is that zeo-lite hinders the more natural nitrogen cycle. In a fully cycled aquarium, beneficial bacteria lives in the filter and changes ammonia into nitrite, and nitrite into nitrate. The first two are highly toxic, but nitrate is only toxic in higher numbers and this is reduced by vacuuming gravel and changing the water. In a fully cycled aquarium, the changes are so quick that the first two chemicals can not be detected in test results and your fish stay happy and healthy. However, zeo-lite will suck up the ammonia and starve the beneficial bacteria, crashing the nitrogen cycle.
Having said all that, zeo-lite isn't entirely bad. No, it typically shouldn't be used in the home aquarium, but there are some situations that zeo-lite can benefit your fish. Sometimes aquariums under 5 gallons have trouble keeping a nitrogen cycle stable. Another acceptable case would be a temporary aquarium, such as a hospital or quarentine tank. Sometimes spare aquariums need to be unexpectedly and quickly set up, and you can not borrow media from another aquarium to jump start the cycle. For these exceptions, empty the filter of any sponges, media, cartridges etc and add zeo-lite. Do monitor the ammonia level carefully, and frequently re-charge the zeo-lite in salt water. Keeping a lot of fish in an aquarium with zeo-lite will make this maintenence more difficult but even more mandatory. Remember, you can not treat fish with salt in an aquarium with zeo-lite.
“Logic will get you from A to B. Imagination will take you everywhere.” Albert Einstein