O'kay. Maybe I'm doing something wrong. I have everything hooked up, and it's working. But, I just don't understand. I have a Rio 1700 for a return pump, which is rated for about 600 gallons per hour at four feet of head. Since the overflow is external, I needed to use a U-tube. The U-tube I got from Alamo is 1 1/8 inch inside diameter. That means it should be good for about 600 gallons per hour. Sounds like I should be able to get by with just one U-tube. But, that's not doing the job.

I am currently using the 1 1/8 inch U-tube, along with 3 others that I rigged up so that it would work without throttling back the pump too much. 2 of the ones I rigged up are 3/4 inch plastic tubing, and the other is 1 inch PVC that I put together with some extra pipe and a couple of 90 degree elbows. With all four of these running, I still have to throttle the pump back a bit.

What's the deal?! Is there something I'm doing wrong? I guess I just don't understand enough about how these things work.

(BTW, the overflow is holding just fine.)