[tkhawaja]

For DSB purposes the garin size seems to matter most. All articles I have read advocate going with a sugar grain size as it provides the "best" real estate for the right kind of bacteria. I would stick with sand specifically for aquaria as "playsand" would not have been FULLY stripped of any metal traces. Also be sure the DSB is populated with flora / fauna to keep it turning. Otherwise bacterial secretions may cause hard lumping.