Dsb

[SpongeBob]

I have a 125 with built-in overflows that pull water 3" from the floor of the aquarium. I understand the need for a DSB to be at least 4" in depth. Can I "average" my depth? For example, 6" in the back, 3" near the overflow intakes, and 3 or 4" in the front?

Or does a DSB need to be a uniform 4+" to be a DSB?

I asked Patrick, but he wasn't sure...

[Boogiechillin]

You can vary the depth a bit with only a minimum loss of function. Those thinner layers won't denitrify as well and will let a little more O2 into the DSB than you would like, but it's unavoidable in this case. You will likely need to set up some kind of boundary around the base of the overflow to prevent the sand from evening out with time - most active beds will shift to a fairly level surface in the absence of strong currents.