In aquariums, Zeolite or Ammogon (a small white granule) is used to remove ammonia from water. And Carbon (a small black granule that is different from charcoal) is used to remove chemicals and heavy metals from water.
Because Zeolite removes ammonia, it removes the food the beneficial filter bacteria eat and this can prevent a filter from cycling (developing the good bacteria needed to keep ammonia and nitrite levels at 0). If you add Zeolite to a tank with an established biological filter, it can stop the biological filter working.
When the Zeolite is full of ammonia, it stops adsorbing it and you get an ammonia spike/ build up, which can kill fish because there is no beneficial filter bacteria to break it down into nitrite and nitrate.
There is no way of telling when Zeolite is full except if you test the water for ammonia every day and you get an ammonia reading. Subsequently, most places that sell Zeolite, suggest changing it every week. This theoretically means it will be fresh and keep ammonia levels at 0ppm for the entire week. It might continue to adsorb ammonia for longer but it's hard to tell when it's full so it needs to be changed regularly.
Zeolite can be recharged by soaking it in salt water and then drying it.
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Carbon can remove plant fertilisers, chemical medications and heavy metals from water. It does not remove salt, calcium or magnesium. If you are treating fish or adding plant fertiliser to the tank, you need to remove carbon from the filter so it doesn't remove these things from the water.
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The best filter media to use is sponge. You can buy sponges in different grades with fine, medium, course or extra course gradients. The different grades just have different sized holes in them and medium grade sponges are commonly used for aquarium filters.
You can buy sponges for various makes of filter and use a pair of scissors to cut them to fit your current filter. AquaClear do nice sponges in a range of sizes and are available from most pet shops. There are other brands too.
Sponges get squeezed out in a bucket of tank water at least once a month and the sponge is re-used. The bucket of dirty water gets tipped on the lawn/ garden. Sponges will last for 10+ years and only get replaced when they start to fall apart.
You can use course, medium and fine sponges together in a filter or just one type of sponge.
You can use bioballs in conjunction with sponges.
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If you change the filter media, add the new media to the filter and leave it there for at least a month with the old media. After a month or more, remove some of the old media and add some more new media. Wait another month and then remove the last of the old media and add new media.
Don't clean the new media for a month or so after it has been added. This will give the beneficial bacteria time to develop a biofilm on the sponge and stick to it properly.
