Zeolite, ammonia and fish health

Zeolites are an ideal means of managing ammonia levels in the short-term until full filter active is restored or achieved. Even modest levels of ammonia are a threat to fish health. This is particularly a problem in new ponds and aquaria where we have to let ammonia levels rise a little to encourage the establishment of nitrifying bacteria in the filter. Elevated ammonia can occasionally be a problem in established set-ups.

What are zeolites?
These are naturally occurring types of minerals, although because of their usefulness as molecular sieves they can now be artificially produced. In their natural form they are aluminosilicates, which are normal silicate minerals containing aluminium. The structure is such that these minerals can loosely bind positive charged ions, usually sodium.
They act as ion-exchangers and 'swap' their sodium ions, for other positively charged ions, for example calcium or ammonium. So they are often used for water softening to remove hardness-forming calcium ions. Fish keepers can make use of this unusual characteristic and employ them to remove ammonia (or more strictly ammonium - NH4+) from the water.

Using zeolite
The required amount is simply placed in the filter just before the water is returned to the pond or tank. Don't place it before the biological section otherwise there may not be enough ammonia left to encourage the growth of nitrifying bacteria.
Depending on the current ammonia levels, the zeolite is removed when it is 'full' and left overnight to soak in a very strong salt solution, during which the collected ammonium is "swapped" for sodium (you will recall that salt is actually sodium chloride). After a good rinse in clean water it is ready for use again

How much and how often?
For aquaria use, zeolite and other ion-exchanger products usually come in pre-prepared pouches with instructions. For pond use it is best to have at least two 10 kg sacks - one in use, the other being recharged.

Initially it will probably need to be changed daily, until such times that ammonia test kit readings show that levels are stabilising. Once this happens the period between cleans can be extended

To clean it use 2-3 oz salt per gallon of water. The actual amount is not critical as long as it is good and salty. It should only be used to manage an existing problem and not used on a long-term 'just in case' basis. First, if used permanently there is always the risk that it will 'dump' its ammonium collection. Secondly, it also acts as a water-softener and will remove calcium from the water.

Initially, even with zeolite it may still be necessary to do partial water changes to keep ammonia at an acceptable level. Zeolite cannot be used in ponds or aquaria where the water is salted