SP,
I think you are going about this the wrong way. I would use your input water to aerate your small pond. Bottom diffusers are used to circulate water to the top and let nature off gas the bad stuff and add O2 to that water. Top water aeration is how O2 is put into water.
Knowing your input pipe, I would design a cap (or caps) that curtained the water as it fell to your pond which would add a lot more O2 to your pond with no additional costs and no maintenance.
PM me if you want more of my two cents on this one, it should cost you about $10 to do it my way.
