Here's an interesting article about aluminum and Phosguard.
http://www.advancedaquarist.com/2003/7/chemistry
From the conclusion of the article.
" Phosguard has been shown to release aluminum to artificial seawater. Further, it appears that the release of aluminum could be the cause of the effects that some folks have seen in aquaria when using aluminum-based phosphate and silicate absorbing materials. "
--- Warning... Anecdotal Info following ---
For what it's worth I used to use Arm and Hammer Baking Soda. I noticed after a while that the Finger Leather Corals(Sinularia sp.) in my tank weren't doing that well. Arm and Hammer Baking Soda is known to have aluminum in it.