▷ Ion exchangers in the aquarium | All information and details

What is an ion exchanger

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As the name suggests, an ion exchanger exchanges ions. There are basically two different processes that lead to water with different ion levels. In the neutral exchange, all cations are exchanged for sodium ions.

Although neutral exchange leads to soft water, it does not change the total salt content. Neutral replacement is therefore useless for aquaristics. Neutral exchangers are regenerated with common salt.

In the case of full desalination, the conductance is also reduced. A desalinator consists of two columns filled with resin.

In the acidic cation column, all cations are exchanged for hydrogen ions H+. In the second step, all anions are exchanged for hydroxide ions OH- in the basic anion column. So what remains is H+ and OH-, makes H2O. The result is almost ion-free water.

The columns are regenerated with hydrochloric acid HCl and sodium hydroxide NaOH. However, diluted acid and diluted lye are used, which are harmless.
The leftovers from the regeneration can be thrown together. Salt NaCl and H2O remain. This slightly alkaline saline solution can be poured down the drain.

Complete desalinators can be adjusted quite well to the respective requirements by using suitable resins. If only a weakly acidic cationic resin is used, only decarbonization takes place.

A strongly acidic resin must be followed by a basic resin because various mineral acids are formed. In conjunction with a weakly basic anion exchange resin, almost all ions are exchanged.

Only the weak acids carbon dioxide and silicate remain. Because the water running off is quite acidic, it needs to be aerated.
The weak acids are also largely removed with a strongly basic anion resin. The more the resin depletes, the more silicate is let through.
The water running off from this combination has a conductivity that can go down to 1 µS/cm and smells quite strongly of the strongly basic resin. A downstream, non-regenerable ultrapure water resin absorbs the odor and reduces the conductance to well below 1 µS/cm.

Depending on the starting water, CO2 usually has to be expelled. This is not necessary with strongly basic anion resins.

Ion exchangers in comparison with osmosis systems

Reverse osmosis systems are fine sieves. They retain approx. 95% of all substances in the source water that are in non-ionic form. This includes e.g. B. also pesticides. The permeate, i.e. the water produced, of a starting water with 20° dGH still has 1° dGH. If the breeding of glow-light tetras is only successful under a carbonate hardness level, but in osmosis water e.g. If, for example, there is still 2° carbonate hardness, an ion exchanger must be used instead of an osmosis system.

Depending on the substance, reverse osmosis systems let about 3 to 7% of the initial amount through. The rest are held back. Almost all nitrates and other toxins are removed. Silicate is also held back, but not as well. In contrast to demineralizers, osmosis systems retain organic substances. Osmosis systems also hold z. B. copper or pesticides back to a large extent. Osmosis systems filter approx. 95% of all non-ionogenic pollutants, e.g. B. pesticides, out of the water. Toxic heavy metals also get stuck in the ion exchanger. Any chlorine present must be removed from the water using a carbon filter.
If you value low-pollutant water, ion exchangers are theoretically not as well suited as osmosis systems. Of course, this advantage only becomes effective if the corresponding substances are also present in the starting water. In Germany, however, there are hardly any concentrations in the drinking water that are lethal for fish.

Water from ion exchangers has even fewer ions than water from reverse osmosis systems. Deionizers produce a conductance below 10µS/cm. In osmosis systems, the conductance is usually somewhat higher. The pH value of demineralizers is clearly in the acidic range, up to around pH 5. The reason for this is the weakly basic exchange resins used, which do not remove the HCO3.

Water production takes much longer with osmosis systems than with ion exchangers. Osmosis systems require less space and require less maintenance than full desalinators, which have to be regenerated regularly with caustic soda and hydrochloric acid.

Osmosis systems must be flushed regularly. The pre-filter may need to be replaced regularly. Above a certain amount of dissolved minerals in tap water, an osmosis membrane can become clogged and become unusable.

The price-performance ratio depends on how much water is needed per year. In osmosis systems, about 4 liters of waste water are produced for every liter of permeate. In principle, osmosis systems are therefore more cost-effective for low water requirements, full demineralizers for high water requirements.

Advantages of deionizers

Once an osmosis system is connected, it can certainly be operated more easily. An osmosis system is perfectly adequate for average tap water and average aquarium water. However, it must be taken into account that 300 to 400% of waste water ends up in the drain, with exchangers only around 10%. With 100 liters of osmosis water, around 300 liters of waste water are produced, instead of around 10 liters with exchangers. That is about 30 times as much waste water. It is a matter of time how long we can afford to waste drinking water like this.

What is a mixed bed exchanger

Mixed bed exchangers are filled with a mixture of cation and anion exchange resins. The fully desalinated water is tapped directly from the water pipe. A LF indicator should be integrated. The company Christ offers e.g. B. a 10 l mixed bed. The resin mixture of these systems is regenerated by service companies after exhaustion. The exhausted resin is given away in exchange for fresh resin. A regeneration station should therefore be nearby.

A provider can possibly be found in the Yellow Pages under the keyword water purification. A mixed-bed exchanger with a cartridge of 10 to 20 liters is usually sufficient. Such an exchanger makes sense with a consumption of less than 3000 liters per year, depending on the water price. With a system dimensioned in this way, approx. 25 l of water can be produced within an hour.

The resin can e.g. B. 2/3 consist of a strongly basic anion exchanger, so that the silicic acid comes out completely. The conductivity of the fully desalinated water is below 2 µS/cm. This is good enough for aquaristic purposes. With a filling of approx. 10 liters, 2000 liters of water can be produced at 10° dGH. The regeneration costs about 30 euros.

Operation of an ion exchanger

Desalination systems consist of 2 columns filled with resin.

Connection of a deioniser

If a flow rate of approx. 30 liters per hour can be set at the tap, the system can also be connected directly to the water pipe. If the water has to go through for a long time, the result is particularly pure water. The throughput decreases over time until it is regenerated again.

Depending on the system, about 1.5 hours are required for 100 liters of water. In small systems, around 60 liters of water are treated per hour. With so-called mixed beds z. B. 200 to 250 liters of water per hour can be treated. That’s about 20 times the speed of a medium-sized reverse osmosis system. If necessary, you can wait until the bucket or canister is full when tapping.

A mixed bed consists of a homogeneous mixture of grains of cation and anion exchange resins. The resins must be cleanly separated from each other so that each resin can be regenerated separately. The quality of the separation determines the quality of the generated, fully desalinated water. This requires a separating system that uses the different densities to separate the two types of resin. This is only possible in professional regeneration systems. Mixed beds are therefore not regenerated themselves. The resins are returned to a regeneration station and exchanged for fresh resins.

A column is a cation exchanger. The other column is an anion exchanger. In the cation exchanger there is usually an indicator resin that turns from brown to red when it is used up. The resin is regenerated with dilute hydrochloric acid. The anion exchanger usually contains beige-colored resin that is regenerated with caustic soda.

The regeneration solutions must flow slowly through the columns. The acid or base slowly runs through the respective column from a canister that is suspended above the demineralizer. The regeneration solutions are then removed from the columns by flushing. If the chemicals are handled carefully, regeneration is harmless. The best way to regenerate is in a shower tray so that acid or lye splashes can be quickly removed with the shower jet. The time required is approx. 45 minutes. The seals of the canisters or containers used must be checked regularly. The caustic soda causes the seals to leak and the acid or lye could leak out in an uncontrolled manner. Teflon seals, e.g. B. Teflon tape, or Viton, should be stable.

Some pet stores offer a regeneration service. Care should then be taken to ensure that the systems have full capacity again after regeneration.

The performance of the systems is given in liters of hardness. This is the amount of water multiplied by the degree of hardness that can be treated by a deionizer before the deionizer needs to be regenerated.

4500 hardness liters means e.g. B. that the system can desalinate 450 liters with 10° dGH, or 225 liters with 20° dGH.

The resins used in the columns are relatively expensive. With careful use, however, they are not used up, but only exhausted. If the resins are carefully regenerated, full capacity can be restored. The chemicals needed for regeneration are relatively inexpensive.

Because the resins do not release any harmful substances into the water, the water from the columns can be used immediately without having to drain the water first.

However, the fully desalinated water must not be fed into the aquarium immediately. It is very low in salt and contains a lot of carbon dioxide. The higher the proportion of carbonate hardness in the total hardness of the starting water, the more carbonic acid the demineralized water contains. To ensure that the water values ​​in the aquarium do not change suddenly, the water must therefore be adjusted to the aquarium water before it is used in the aquarium.
Fully desalinated water is significantly less salty than…