Ted
If I were you I would get a glass/ceramic diffusor from the Rhinox range. Aquatic Magic sell them on ebay. (I have 2 at the moment 1 is a spare)
They works as follows:
Rhinox 1000 - under 20 gallon tanks
Rhinox 2000 - 20-40 gallon tanks
Rhinox 5000 - 40 gallons upward.
I don't know what setup you are using but these will work better with a pressurised setup. They do work well with yeast though (although the advert says not. lol)
1 nutrafin or DIY will work with the 1000, the 2000 wil need 3 nutrafins or 2 DIY (I used to run 2 nutrafins + 1 DIY into my 2000 and it worked fantstically well)
They are quite cheap and he ships worldwide.
Now I've given you some advice, I've added pics of my new additionsto the thread you answered last night. Not great pics but can you have a look at them for me. Many Thanks
Andy
EDIT: I se you have the same tank size as me so its the Rhinox 2000 for you.
Andy