Honestly I had never heard about before. I had inquired with Ply Bio Marine about their product (Poly Filter) in regards to removing aluminum (leached from one of those phosphate filters!) and this is what they said:

Karin,

The activated alumina products sold into the pet industry and then repackaged as
phosphate adsorbents leach aluminum ions and alumina particulates.
Activated alumina products should never be directly added into saltwater reef aquaria.
Our food grade activated alumina for potable water system is pre leached in sterile
ultra pure water. However, we still only recommend it in our Kold Ster-il (r) System not
used directly in saltwater aquaria applications

You should also be aware that the Iron (ferric hydroxide ) granules and pads also
have negative effects upon saltwater. Like activated alumina ferric hydroxide adsorbents
will adsorb alkalinity and specifically trace elements. The main trace elements adsorbed
are Vanadium, Copper and Rubidium plus alkalinity. In the future you should consider
our Poly-Filter (r) will sorb all phosphates : Ortho, Poly, Tri Poly, Hexa-Meta and Organic .

Poly-Filter (r) will sorb the alumina solutes (dissolved aluminum) but not the
free particulate alumina. Particulate alumina oxide removal requires a very
specialized particulate filter i.e. one micron or smaller particulate filter system.
The quickest approach is as follows: remove each leather coral and rinse well in
aluminum / alumina free saltwater . While the leathers are out of the aquaria use
Poly-Filter (r)( for the aquarium)to sorb aluminum solutes in concert with a large diatom
filter system. Yes ,in this emergency situation, use the diatom filter with it's silica based
medium. You will have some diatom growth later. If you soak the diatom media in R/O
or low pH distilled (copper-free) water before usage much for the free silicates will leach out.
The high pH and alkalinity of saltwater reef aquaria would prevent most of leachate silicates
from entering solution. Instead they will simply precipitate out onto the bottom.
We do manufacture a specialized 0.20 micron filter canister and media that would sorb
any alumina particulates and dissolved aluminum ions. However, by the time you could order
a strong pump and our Fin-L-Filter (r) PSM-1 System the leather corals will be severely
effected and damaged.

The quickest approach is: leather coral removal, rinse corals well, Poly-Filter (r)
plus a large diatom filter used for aquarium filtration / alumina solute, particulate
removal.