Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
Cationic Exchange Capacity is a way that fertilizers bind to the soil particles. That is the reason we use high CEC substrates. These substrates hold the fertilizers until the plants do something (exchange cations) to release the fertilizer.
You could try a weed mat sort of stuff, it would keep things separated. Impossible to work with to plant, though, and if it starts working its way up anywhere you will have to redo a major part of it to put the little bit back where it came from and make it stay there.
This is not a new concept, and many materials have been tried over the years. Mostly the method is not used because it causes more problems than it solves.
Very roughly 2 wpg of T-12 = 1 wpg T-5, but this is rough, depends on reflectors and the actual wavelengths of the bulbs. Often T-5 fixtures, designed for aquarium use, have much better reflectors than the T-12 set ups.