Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
Set a fountain pump or power head as low in the tank as you can.
Aim it as vertically as you can. Optimum location is wherever there is the least water movement from the filter. In a case where there is no equipment already creating some water movement then the bottom middle.
This will create a rising column of water.
It does 2 things:
Takes the 'worst' water, from lower in the tank and sheets it across the surface for maximum air contact.
It adds more ripples to the surface, increasing the surface area.
You can get the same effect from an air stone, but I think the pumps move a lot more water.