GFO vs. Aluminum Oxide


Active Member
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Jul 12, 2014
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Denver, CO
Over the past 6 months I've been using BRS high capacity GFO, but I feel like its too fine grain for my media reactor(IM mid-size) and slows the flow down drastically. I switched to SeaChem Phosguard as it doesn't clog my reactors as badly, but I haven't noticed significant performance from either.

What are the pros and cons of each?

Randy Holmes-Farley

Reef Chemist
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Sep 5, 2014
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Arlington, Massachusetts, United States
Both work, if you use an appropriate amount and replace it soon enough.

GFO is usually somewhat more expensive and can release some iron tot he system. That iron can cause precipitation of calcium carboante on or downstream of the GFO. The iron may also supply iron to good things (macroalgae, corals, etc) and bad things (cyanobacteria).

Aluminum oxide can release aluminum, which has been known to irritate certain corals, such as leathers. There's soem debate whether this released aluminum is very fine particulate or individual aluminum ions. In a sense it doesn't matter, but I think it may be both. People doing Triton testing can now often detect the aluminum rise in their water when using aluminum oxide binders or other objects. It is also larger sized media, which can be an advantage.

I've used both, and if you do not see any irritated corals, either choice may be fine. I currently use GFO and not aluminum oxide. I also dose soluble iron.

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