Reaktormedien unter der ICP-OES-Lupe

09.03.2019                                                                                    

Reactor media such as activated carbon, zeolite or phosphate adsorber are often used in reef aquariums. We are interested in what elements and in which quantities of these reactor media are released into the water, and whether frequently stated statements such as "phosphate adsorbers give barium to the water" are actually applicable.

For this purpose, we swirled 2 different zeolites, one activated carbon and two commercially available iron-based phosphate adsorbents (GFOs) in standardized seawater for 72 hours, then filtered the samples, and then analyzed using ICP-OES. So we can determine which elements are released by the media, or even taken from the water.

 

This knowledge helps us to better interpret your seawater analysis, and to give targeted solutions. Of course we want to share interesting results of this "mini-study" with you.

At this point it should be mentioned that in each case only one sample of the respective media was analyzed. Of course, there may be variations between different batches and manufacturers of reactor media. This article serves to show what *can* be released by the media to the water. We plan to expand the lineup in the future, explore more media, and stay abreast of results.   

 

But now to the results, let's start with barium.

Like calcium and strontium, barium is an alkaline-earth metal. Therefore, barium is incorporated in the skeleton of stony corals in the same way as these two elements are, or it is deposited as carbonate. Barium occurs in natural seawater at a concentration of about 7-15 μg/l. In aquariums, the measured concentration is often much higher, usually phosphate adsorbers are believed to be the main source of barium.

The zeolites were the main barium source in the media we examined. With an used amount of 1 kg per 1000 l  (1 g/l), the zeolite increased the barium content by 41 and 82 μg / l, respectively.  This already shows that there are large differences between the zeolites. - We are looking forward to testing more zeolites in our lab.

 

The investigated activated carbon does not introduce any appreciable amount of barium. Although phosphate adsorber 1 released barium to the water, it is significantly lower than the investigated zeolites, while phosphate adsorber 2 adsorbs barium, thus even reducing the barium concentration. 

Now to another element, which is in a topic of  reef aquariums again and again, the silicon. Silicon is not necessarily problematic in the reef aquarium (but even important for skeletons for sponges), but the growth of troublesome diatoms can be promoted by high silicon concentrations.

 

As a source of silicon, the starting water is assumed in most cases, since silicon (or silicates / silica) in tap water often occurs in very high concentrations, and is not completely removed by reverse osmosis systems. -  For this reason, in addition ion exchange resins are used to remove the residues of silicon from the starting water. But is the source water the only source of silicon?

According to our measurements by no means, because the examined activated carbon, with a use quantity of 1 g / l lead to a silicon increase of over 800 μg/l.  The investigated zeolites, as well as phosphate adsorber 1 lead to a silicon entry into the aquarium water. Phosphate adsorber 2 slightly reduced the silicon concentration.  These results are quite surprising for us, and we use them as an opportunity to examine more activated carbons.

At this point we would like to emphasize again that the results do not mean that all activated carbons release large amounts of silicon to the water - it is only a random sample! 
 

What advice can be derived from these results?

 

We recommend to soak the reactor media before use, and to rinse thoroughly with RO water as this can significantly reduce the input of silicon and / or presumably barium.

We will supplement this article with data from other elements and media. - Stay tuned!

 

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Many Greetings, 

Your Oceamo team