If you are going this route I would suggest skipping MarinePure and going with Sera Siproax. Stuff is much better IMO.
I agree with you, but Siporax is MUCH more expensive and harder to get. But sintered glass is a better substrate than aluminosilicate foam for a few reasons.
I have a 8/8/4 block I put in my sump 2 weeks ago. Monitoring nitrates as we speak. Will post here with updates.
Corey
My plan is to use them in my sump as I like the look of a little less rock in the display tank.
Concerning them becoming nitrate factories I don't understand this. They do not produce nitrate from nothing. The bacteria in them break down the much more harmful ammonia and nitrite. If you want less nitrate start with less ammonia, or carbon dose.