I have a couple of Rena pumps - the 200 runs an air curtain in my 2ft and a small cannister filter in my QT tank. I also have a 50 which runs my brine shrimp tank. Both are very quite as long as you make sure the outside of the pump doesn't touch anything.
One thing I did find with the Rena on the air curtain was that it was better if you put in an valve on the air line (as well as a non return valve) so that you can adjust the amount of bubbles you get - Renas (apart from the 50) have an adjustment screw but I found a valve on the line was a lot easier to use.
I like the bubbles in my tank - I put the curtain across the end of the tank away from the heater and filter. I am in the process of planning a new tank and I will definitely be making room for a bubble wall!
Cheers, Eddie
