Aluminum oxide removal
Some time ago European hobbyists began using a new approach to phosphate removal. Instead of using aluminum oxides to remove phosphates, they began using ferrous (iron) oxides. Advocates of iron oxide phosphate removers argue that iron oxide has two primary advantages over aluminum oxide for removing phosphates. First, it can remove a greater proportion of phosphate enabling hobbyists to reduce phosphates to lower levels than they can with aluminum oxide. Secondly, they point out that iron oxide phosphate removers contain no aluminum. The iron oxide based products began appearing on American shelves last year, and initial reports have been very positive.
The two best known products available in North America are Two Little Fishes PhosBan and Rowa's Rowaphos. Both products are iron oxide based, but there are physical differences between the two products. Rowaphos is wet with a caviar- like appearance. The manufacturer recommends keeping the material moist and the container tightly closed. Phosban particles appear similar from a distance, but under the microscope look quite different (figure1). It ships dry and there are no cautions about its storage. Both materials are quite fine and can end up dispersed in the tank if a hobbyist is careless in securing the media. Fortunately both products include filter bags to contain the media. Recommended dosage differ somewhat. Rowaphos recommendations are based on volume. They recommend 2 milliliter per gallon of saltwater. In contrast, Phosban recommendations are based on weight. They recommend 1 gram for each gallon of water. I paid about the same for one hundred milliliters of Rowaphos and 150 grams of Phosban, so using the respective company's recommendations, the smallest package of Rowaphos will treat 50 gallons while Phosban will treat three times that volume.
To test the effectiveness of Phosban and Rowaphos, I used both products on small test tanks filled with water from mature heavily fed reef tanks. One test run used water from a tank with orthophosphate levels that could only be detected using a spectrophotometer. The second run used water from a tank with levels easily detected by a hobbyist test kit like Salifert. The test tanks held a little over two gallons of tank water. Five grams of each media were sandwiched within filter media and placed in Marineland Duetto internal filters. Orthophosphate levels were measured using a Hach DR4000 Spectroradiometer. Phosphate levels were measured at the start and then hourly until levels failed to decline further, generally about seven to eight hours.
The bottom line is that both products work, and using similar quantities of material work similarly. Figure 2 shows the results. Each product reduced phosphate very quickly and ultimately lowered levels by two thirds. At these levels, phosphate was undetectable (to my eyes) by the Salifert test kit and at the detection limit of the spectroradiometer. The second run began with phosphate levels twice as high as the first run. Again, the products performed similarly (data not shown). Orthophosphate levels dropped to less than 0.02 mg/l, which while 50% less than initial levels is still higher than recommended. This suggests that the media was exhausted.
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