What is the size of your setup?
If its 50g+ then normal diffusers wont be effective for it. Forget it if you are running a sump.
I highly suggest a reactor(you can make one too), last one I tried was ISTA mixmax/turbo, it works like a charm with a powerful pump/powerhead.
Up Aqua and JBL(I believe both are same in different packages) inline atomizers come in 16-22 hose size, you have a sump system so you can reduce the pipe size a bit. Good thing is, they do not hinder the flow at all even if placed on the outlet hose from sump.