More than reducing the turbulance caused by the AquaClear, what I want to reduce is the amount of breaking the AC does on the surface (agitation). Over the course of the week, as the water level drops a bit due to evaporation, the AC causes a lot of surface agitation. So I want to keep the surface calm during daytime. At night I run a sponge filter to help re-oxygenate the tank.
The tricks that I mentioned work well. The filter material placed on the spillway keeps the surface really calm. Phil Edwards showed me this trick. If you cut the filter material long enough; it will help with agitation due to evaporation. You can always add water to your tank as needed to keep it full. I usually have my tanks filled to the place where the glass cover fits. I like open top tanks though. The filter material I have used is made by Purolator. I get two sheets for $2 at the local hardware store.
Purolator
Washable Room Air Conditioner Pad
15" x 24" x 1/4"
CYS - 2 Pack
Part # 191773
UPC 049403020833
It's a dark grey color
The blue bonded filter material is a little thicker and it cuts down on turbulance more.
Coralife Pure Flo Filter Pad (18"X24") at Big Al's Online
Left C - the baffle you refer to, I think, helps reduce the current inside the tank. But I'm not sure if it'll help eliminate the surface agitation.
It does reduce the current and when used in tandum with the filter material on the spillway gives you a fairly calm surface.
Here's the instructions for the Hagen AC.
http://www.hagen.com/pdf/aquatic/Aquaclear_English.pdf
Go to page 6 of 9 and look at diagram 4 and check out the little "magnified" view. It shows how the intake tube fits on the grey piece of plastic
but it doesn't show the little nub that I mentioned that can be ground off.
Diagram 6 on page 7 of 9 shows how you adjust the flow.
These mods only cost a few pennies to do but if you want the Eheim 2213, go for it.