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7.4.3. Ionenwisselaar harsen

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Auteur : David Bogert

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There are two distinct uses for deionizing resins. One is to treat water for a water change and one is to directly treat the aquarium water to remove nitrates or ammonia. Neither use is a very good use of monetary resources, to put it mildly. What is DI (Deionizing or Ion Exchange) resin? An ion-exchange ... Lees meer

There are two distinct uses for deionizing resins. One is to treat water for a water change and one is to directly treat the aquarium water to remove nitrates or ammonia. Neither use is a very good use of monetary resources, to put it mildly.

What is DI (Deionizing or Ion Exchange) resin?

An ion-exchange resin or ion-exchange polymer is a resin or polymer that acts as a medium for ion exchange. It is an insoluble matrix (or support structure) normally in the form of small (0.25–0.5 mm radius) microbeads, usually white or yellowish, fabricated from an organic polymer substrate. The beads are typically porous, providing a large surface area on and inside them. The trapping of ions occurs along with the accompanying release of other ions, and thus the process is called ion exchange.

There are multiple types of ion-exchange resin. Most commercial resins are made of polystyrene sulfonate. Polystyrene sulfonates are polymers derived from polystyrene by the addition of sulfonate functional groups. They are widely used as ion-exchange resins to remove ions such as potassium, calcium, and sodium from solutions in technical or medical applications.


This is a very accurate description of DI resins.

Otopharynx ovatus Chilumba
Otopharynx ovatus Chilumba

Using DI Resins to Treat Aquarium Water

“DI Resins” are synthetic porous polymers that “deionize”. These include such products as Countryside C3 resin and NO₃Go resin. There are two basic types of resins. One is a “anion” exchange resin. Anions are negatively charged ions such as nitrates and nitrites. The other type of resin is a “cation” exchange resin. Cations are positively charged ions such as ammonium.

As an example of how a resin works look at the cation filter media out there which claim to remove ammonia from the aquarium by exchange with sodium in a resin bed. Cations include sodium, ammonium, potassium, magnesium and calcium. The claim is that these resins remove the ammonia as ammonium.

While that is true, one must understand that the resin is “non-selective” and will “exchange” for every cation in the water, not just ammonium. So, let’s look at a typical Amazonian aquarium with 100 gallons of soft acid water. It will have in it roughly 4 grams of sodium, magnesium and calcium, which is VERY low. Let us arbitrarily say this aquarium has 4 grams of ammonium (which is very high, 12 ppm). Let’s add a hanging filter on the back with a generous dose of 1/2 pound of resin.

Sciaenochromis fryeri OB bosbes
Sciaenochromis fryeri OB bosbes

Resins will have about 5 milligrams of exchangeable sodium per gram of resin. 1/2 pound is roughly 200 grams, so the resin will have about one gram of exchangeable sodium in it.

The exchange will take place until the ratio of each cation is the same in both the water and the resin. So the resin will go to 0.5 grams of sodium, magnesium and calcium and 0.5 grams of ammonium. The ammonium level in the aquarium goes from 4.0 to to 3.5 grams. Whoops! That is not a big change. And this is for very low salt concentration water!

If we look at a Lake Malawi aquarium the situation gets worse, MUCH worse. The typical Malawi aquarium water will have roughly 50 grams of sodium, potassium, magnesium and calcium. If there was 4 grams of ammonium, then the resin would drop the ammonia to 3.92 grams.

So resin is pretty useless. This analysis also holds for most anion exchange resins.

Aquarium Fish Nimbochromis venustus
Nimbochromis venustus

A Resin Which Seems to Work for Nitrates

A reader made me aware of a selective anion resin which supposedly selectively removes nitrates. The resin is Purolite a520e (or PA202). The reader has used this successfully to reduce 20 ppm nitrate to 3 ppm nitrate. I haven’t tested it but it looks very promising. AND it is relatively cheap and easily regenerated.

Note that there is a white granular ground up mineral called zeolite which can selectively remove ammonia. But the cost to remove even tiny amounts of ammonia is prohibitive. This product is NOT a synthetic resin. This material is covered in this link:

7.4.4. Zeoliet

There are some biofiltration products that combine activated carbon with resins. These are extremely expensive products. As shown above they can have only a very small effect on the chemistry of an aquarium. A 25% water change is much better and much cheaper.

Peacock Eureka Red
Peacock Eureka Red

DI-harsen om water te behandelen Water verversen

DI is often unnecessarily used after RO systems to remove everything ionic that the RO missed. DI is “deionizing”. It substitutes hydrogen ions (H+) for sodium, calcium etc. and substitutes hydroxyl ions (OH) for sulfates, chlorides, etc. There is NO reason to have a DI resin system added to an RO system.

Merk op dat er veel marketinghype is over deze harsen die sommige mensen lijken te geloven. DI harsen worden veel gebruikt in zeeaquaria (als je de marketinghype gelooft!) om te "dechloreren", om "zware metalen te verwijderen" en om "deeltjes te verwijderen". Dit is allemaal een marketinghype die keer op keer herhaald wordt door goedbedoelende maar slecht geïnformeerde hobbyisten.

Protomelas taeniolatius Rode Keizerin
Protomelas taeniolatius - Rode keizerin

Ten eerste vernietigt chloor DI-harsen, dus niemand zou ooit dure DI-harsen moeten gebruiken voor ontchloring. Ten tweede zijn er GEEN zware metalen die verwijderd moeten worden in drinkwater. Ten derde doen DI harsen NIETS tegen deeltjes. En het feit dat sommige slecht geïnformeerde hobbyisten in de marketinghype zijn getrapt en deze systemen hebben aangeschaft, maakt de marketinghype nog niet waar.

The number of ions in reverse osmosis water is typically in the 10 to 20 TDS range. Removing those dissolved solids (which are present as cations and anions) is just not necessary nor even desirable for ANY aquarium. RO water needs to be “remineralized” to 50 to 60 TDS even for blackwater aquariums and the exact ion mix is of NO importance WHAT-SO-EVER.

Vieja bifasciatus Rio Grijalva
Vieja bifasciatus – Rio Grijalva