from the artical
Inputs of Aluminum in Reef Aquaria: Phosguard
Many aquarists claim to see undesirable effects on corals when using Phosguard, made by Seachem. Many aquarists have attributed that effect to released aluminum, since it is largely composed of aluminum oxide (possibly with silicon present too). In the first phase of testing that hypothesis, I examined whether Phosguard does indeed release any aluminum into solution.
Table 4 summarizes the results for a serious of samples in which commercial Phosguard (75 mL) was placed into contact with aquarium water or freshly made Instant Ocean artificial seawater (500 mL). The samples we allowed to sit in closed plastic containers. Once every 3 days or so the containers where gently shaken for a few seconds. Aliquots were removed, in some cases filtered through a 0.45 ¦Ìm filter to remove ¡°particulates¡±, and the aluminum was determined by ICP (without acidification). The concentrations were determined by comparison to standard made by spiking 0.5 ppm aluminum into aquarium water or Instant Ocean artificial seawater (which had been shown earlier in this article to have no detectable aluminum). All of the samples had a clearly definable emission peak in the appropriate place, although the lowest sample (0.06 ppm) is close to the limit of detection.
Table 4. Aluminum Concentration in water samples exposed to Phosguard
Water Sample
Exposure Time
Filtration
Aluminum Concentration (ppm)
Aquarium Water
none
none
¡Ü 0.05
Aquarium Water
1 week
none
0.37
Aquarium Water
1 week
0.45 ¦Ìm
0.06
Aquarium Water
5 weeks
none
0.71
Aquarium Water
5 weeks
0.45 ¦Ìm
0.12
Instant Ocean
none
none
¡Ü 0.05
Instant Ocean
1 week
none
1.11
Instant Ocean
1 week
0.45 ¦Ìm
0.13
From the results in Table 4 it is evident that Phosguard does release aluminum to the water, and that the majority of this is present in particulate form (that is, that it is removed on a 0.45 ¦Ìm filter (although that does not demonstrate that it was originally released as particulates).
In order to determine if these results are caused primarily by fine particles that come with the much larger Phosguard particles (typically about 2 mm spheres), a batch was rinsed very thoroughly with RO/DI water (8 times, with each rinse lasting about 1 minute and each rinse volume comprising about 20 times the solid particle volume). These rinsed Phosguard particles were then exposed to aquarium water as above. The results are shown in Table 5.
Table 5. Aluminum Concentration in water samples exposed to rinsed Phosguard
Water Sample
Exposure Time
Filtration
Aluminum Concentration (ppm)
Aquarium Water
none
none
¡Ü 0.05
Aquarium Water
2 weeks
none
0.25
Aquarium Water
2 weeks
0.45 ¦Ìm
0.16
Not surprisingly, the concentration is reduced in the unfiltered sample, indicating that the rinsing may well have removed some fine particles that were contributing to the results in the unfiltered samples. However, the aluminum concentration in the filtered sample is not reduced, indicating that the ¡°dissolved¡± fraction of the aluminum is not altered by rinsing the Phosguard first.
Significance of Aluminum Release from Phosguard
Is the amount of aluminum released from Phosguard significant? Moreover, is it adequate to explain the results on corals that have been reported by aquarists? This question is extremely difficult to answer without some biological experiments. The tests run above show reasonably high concentrations of aluminum. Possibly high enough to cause problems for the organisms shown in Table 1 . But these tests were carried out on a large amount of Phosguard in a small amount of water. Tests with larger volumes of water might well result in lower aluminum concentrations. Additionally, the exact nature of the aluminum in these tests may well be different than in the toxicity tests reported above. That is, the nature may be particulate vs. colloidal vs. soluble vs. complexed by organics, etc.
