Do you reccomend BDBS or a CEC substrate or somethingelse?
I'm of the opinion that CEC means nothing in an enclosed glass box, but if it means something to you any calcined (kiln fired) clay product such as Turface is good. Otherwise, any 2-3mm non-coated material works just fine if you plan on primarily dosing the water column. I haven't used it myself, but lots of folks have success with BDBS so it seems to be a safe bet. If you prefer nutrients via the substrate then go with an inch or so of 50/50 calcined clay mixed with sieved organic potting soil, such as MiracleGro's Organic Choice product, capped with 2 inches of Turface. Sieving out the large chunks and capping it are essential.