Cryptic Fuge in Overflow

[ReefGeezer]

I have an overflow section that holds about 5 gallons of water. It has two Durso overflow tubes and takes in water near the top of the water column. I am considering adding some rock in the bottom of the overflow and covering it to reduce direct light in hopes of creating a cryptic zone. Anybody out there ever do something like this.... How did it work... Pros and Cons... ect.? Thanks.

 

[lapin]

My sump is under my tank. I have a semi cryptic zone. No real light but not pitch black. In the middle section I placed some rocks in a basket and ordered some cryptic sponges and stuff. It now has a bunch of weird stuff and a lot of a green coating on everything which I assume is some sort of bacteria