Ok, I have a chiller that is rated for 100min to 400max GPH flow rate thru it. I have a Mag Drive 5 pump that is pushing the water thru the chiller. At a 4ft head it says 310gph. I used 3/4 in PVC for the intake and return. I have a total of 4 90degree elbows on the PVC, 2 on each piece to get over the wall of the aquarium. The rest of the line is 3/4 inch flexable tubing. My problem is the chiller is not cooling. I have returned the original one which worked for about three months, and gotten a replacement and the same thing happens. The chiller unit is rated for a max of 100gal tank I have a 55gal. My question is do I have to much or to little flow? Is there a way to find out exactly what my flow is? I know this might be a hard one to answer but I need some help I am really starting to get fustrated. Thanks everyone.