ReefD, 54 gal corner bow AGA RR, I have a gatevalve installed between the overflow bulkhead and the sump specifically for this reason. It was a tight fit to get the valve in, but just squeaked by. Like you am planning a algea refugium so small reduction in flow would be ok and plan to use the gate valve to do just as you stated above, raise the flow in the box slightly to eliminate the flushing noise. Not sure what the aquaSilencer is? Is this the unit that is similar to the durso, but supplied by megaflow as their brand? If so I have this installed. I have everything plumbed and will be wet testing today/tomorrow. Also have a closed loop installed with OceansMotions 4 way squirt and panworld 50x pump. Drilled 6 holes, 3 in each side. 1 each side for supply (1") and 2 each side for return (3/4"). With my mag 5 running my sump am planning around 15x tank turnover volumn. Also will have the freedom flow box with skimmer and mag 7 pump HOT in the tank which will get me in the neighborhood of 20x turnover. Should work pretty well. All real tight to plum into and under the 54 gallon stand.