If the current in your tank is too strong, try breaking it up with some floating plastic plants, and placing lots of obsticals in the path of the current. I've a Penguine 330 on a 20 gallon high, and it does pump out a strong current in a barren tank, so what I've done is at the point where the current is turned downwards by the glass and starts rebounding, I've made a wall of green plants (I use fake plastic, I'm sure the current might rip some live ones) and along the bottom I've stacked up lots of rocks and caves.
This "wall" is more in the middle of my tank, not totally against the back glass where most people stack their decorations. A lot of the plants are tall as well, so their tips break into the waterfall as well, further reducing the current. I've been able to create slow moving zones in my two back corners by placing large decorations katty-corner in them (some replica tree stumps and driftwood) so that behind them are calm areas.
The fish seem fine. Usually fish will adapt to a stronger current by putting on more muscle mass the way a human doing heavy lifting "bulks up." They adapt. They would also require extra food for the exertion. But if you break the current up with lots and lots of strategically placed decor, most of the fish will find a quiet area to rest when they don't feel like playing in the faster moving water. Non-toxic food coloring can help you determine where the water is flowing exactly.
I turn my airpumps of at night. I find the humm slightly annoying. I think the fish like having the bubbles off too, since they seem to crowd less when the pump is off.
~~Colesea