M@T!@$
DN328
millerkid519
Angelphish
kno4te
Use small pumice rock. I've compared Matrix, de*nitrate, eheim substrate pro, pumice rock, lava rock and none have pores which go deep enough to penetrate all the way through the media. Matrix and de*nitrate are bleached pieces of pumice.
Biohome is the only media which is truly porous. It's pores are long enough so that you can actually blow air through the media (with resistance) ... like a tightly folded or rolled-up T-shirt.
Here, I've compared seachem de*nitrate to pumice rock of similar size and shape. The de*nitrate is bleached white and to the left of each pumice piece ... except for the top two pieces which are reversed (pumice on the left, de*nitrate on the right).
Pumice is the best deal by far. I ordered mine on eBay ... 5 gallons worth or 25.2 lbs for $30 free shipping.
I'll add a higher resolution photo. It got degraded some in the upload.