Anyone heard of this substrate setup?

[Ximat]

A customer of mine said another LFS in the state set him up with a substrate setup like this:

(from bottom up)

Eggcrate - Bioballs - Crushed Coral - Sand

I've never heard of it, nor do I understand any bennifits of it.

 

[RMPD109]

Sounds like a modification of a plenum. It normally consisits of the eggcrate and a type of screen and DSB. I have not heard of the combination you listed though. It would be thick base though.