I have had the same problem with 3 different pumps. I have a decent size loop with a 250ml res. I'm cooling my ram, cpu, and 2 gpu's as well. The problem is that when I turn my rig on, the water seems to flow just fine for about a minute or 30 sec. But then the flow seems to drop off dramatically to just a trickle. I mean the water is still moving but it just slows to a crawl. I have tried using 3 different pumps with the same result. A 655 pump, 355 pump, and an all in one pump/res which I believe is a 655 as well. I know my psu is adequate because I'm using a 1200w Corsair AX. My watts never go above 800 for the total system draw. I even took my main psu out and installed another Corsair AX 1200 and still got the same results. I thought there may be an obstruction but if there was one, wouldn't it be blocked even from the first time I started my system. At first start, the flow is strong and normal. Nevertheless, I took the loop apart to check for any obstructions but I could find none. Do I just need to get another pump for a dual pump setup to keep the flow strong? The system is in a Switch 810 and I am using Primochill's rigid tubing for most of my loop with some crystal links on my ram and cpu blocks. I have quite a few bends in the loop but no more than are necessary for the loop to do it's job. Any advice would be appreciated on how to fix this. Thanks!